<P> Lexie feels guilt following George's death, having abandoned their friendship after he failed to reciprocate her romantic feelings towards him . Mark comforts her, and she eventually agrees to move into his new apartment with him . Thatcher is admitted into the hospital with liver failure stemming from his former alcoholism . When Lexie is found to not be a suitable transplant candidate, Meredith steps in and donates part of her liver, not to help Thatcher, but to spare Lexie the grief of losing her father and because Lexie inappropriately pulled Meredith's medical files and begged her to . Mark and Lexie receive a shock when a pregnant teenage girl named Sloan Riley shows up claiming to be Mark's daughter, and her parentage is soon confirmed . Mark quickly agrees to let her and the baby move in permanently without consulting Lexie, resulting in her ending their relationship when Mark asks her not to force him to choose between Lexie and his child and grandchild, because he'd have to choose them instead of her . She engages in a one - night stand with Alex, but feels guilty and confesses to Mark when he attempts to restart their relationship once his daughter leaves . Mark is furious with her, officially ending their relationship . Despite secretly suppressing her feelings for Mark, Lexie and Alex assume a casual relationship, that Lexie begins to take too seriously and flaunts to make Mark jealous . Lexie is able to use her eiditic memory to help Alex with several of his cases . Meanwhile, Mark and Lexie never seem to get their timing right, with Lexie disinterested and angry at Mark when he wishes to reconcile, or Mark being caught sleeping with a flavor of the day when Lexie wants to rekindle their relationship . Lexie takes part in a surgery on a patient named Alison Clark (Caroline Williams) and informs her husband Gary Clark (Michael O'Neill) that it was a success . However, moments later Alison suffers a stroke and falls into a coma that she is deemed unlikely to wake from . As Alison had signed a DNR form, Lexie is forced to turn off the machine keeping her alive, despite Gary begging her to stop . After failing in an attempt to sue the hospital, a grief - stricken Mr. Clark later returns to the hospital with a gun, seeking revenge on Lexie, Derek and Richard Webber (James Pickens, Jr .). After witnessing Mr. Clark shoot a nurse dead, Mark shields Lexie during the shooting and the pair attempt to save a critically wounded Alex . Seeking supplies, Lexie heads out into the hospital and comes face to face with Mr Clark who attempts to shoot her, but she is saved by a SWAT team member who wounds Clark at the last moment allowing her to escape . Lexie and Mark proceed to save Alex's life, but Lexie is disappointed and when a delirious Alex calls for his ex-wife, Izzie, while nearly dying instead of Lexie . After a showdown with Richard, Gary Clark eventually commits suicide, having killed eleven people and wounding another seven, as well as causing Meredith to suffer a miscarriage . </P> <P> Lexie has a psychotic breakdown after the shooting due to PTSD and a lack of sleep . She is admitted to the hospital's psychiatric facility and is sedated for over fifty hours, with Meredith remaining by her side . Alex, on the other hand, breaks off his and Lexie's relationship because he cannot handle having to help and care for a person going through PTSD and he enjoys sleeping with women that find having been shot, attractive . Lexie, after getting healthy, confronts Alex and knocks him down a peg by telling him the reason he is alive is because of her . She also no longer gives him her "Lexipedia" talents to help on cases . Lexie is irritated that others may view her as fragile and incompetent due to her PTSD and works hard to repair her image, doing so by saving a woman from being paralyzed when no one else saw an issue . She continues to gain her confidence throughout the season and helps an attending discover a cure for hospital fistulas . After both realize they continue to have feelings for each other, Lexie and Mark resume their relationship, but their brief happiness is over when Lexie discovers that during their breakup, Mark had impregnated his best friend Callie Torres (Sara Ramirez) and she again ends their relationship because she is not ready for children, nor does she want to share a child with another couple . Eager to win Lexie back, Mark recruits his protégé Jackson Avery (Jesse Williams) to try to bring him back into Lexie's favour, but his plan backfires when Jackson and Lexie develop romantic feelings for each other, resulting in them starting a relationship of their own . Mark is furious and tries to win Lexie back, but shortly after, Callie is involved in a car accident and Lexie consoles Mark . The next episode, Lexie explains that she will go back to Mark if he continues to pursue her, but she believes they ultimately aren't suited and will be unhappy . Mark agrees to let her go, giving her and Jackson his blessing . </P> <P> Although initially happy in her relationship with Jackson, Lexie is distraught when she learns that Mark has begun a relationship with a woman named Julia . At a charity softball match, her jealousy gets the better of her, resulting in her throwing a ball at Julia . Sensing that Lexie is still in love with Mark, Jackson calls off their relationship . Lexie begins working with Derek's service and becomes increasingly proficient in neurosurgery, helping Derek with a set of "hopeless cases" - high risk surgeries for patients who had otherwise run out of options . During a surgery, Derek is called away on an emergency, leaving Lexie and Meredith to carry out the procedure on their own . Though Derek had instructed them to merely reduce the patient's brain tumour, Meredith allows Lexie to remove it completely, despite not being authorized by either the patient or Derek to do so . The sisters celebrate the successful surgery, but when the patient wakes up, Lexie is devastated to discover that the patient suffered severe brain damage, losing the ability to speak . Alex, Jackson and April Kepner (Sarah Drew) move out of Meredith's house without inviting Lexie to join them, and with Derek and Meredith settling down with baby Zola, Lexie begins to feel increasingly lonely and isolated . After being left babysitting Zola on Valentine's Day, she decides to try to salvage her relationship with Mark . However, after plucking up the courage to visit his apartment, she finds Mark studying with Jackson and loses her nerve, instead claiming that she was visiting to set up a play date for Zola and Sofia . When Mark confides in Derek that he and Julia have been discussing having a baby, Derek warns Lexie not to miss her chance again, resulting in her professing her love to a shell - shocked Mark, who merely thanks her for her candour . He later confesses to Derek that he feels the same way, but is unsure about how to go about things . Days later, Lexie is named as part of a team of surgeons that will be sent to Boise to separate conjoined twins, along with Mark, Meredith, Derek, Cristina and Arizona Robbins (Jessica Capshaw); however, while flying to their destination, the doctors' plane crashes in the wilderness . Lexie is crushed under debris from the plane, but manages to alert Mark and Cristina to help her . The pair try in vain to free Lexie, who realises that she is suffering from a hemothorax and is unlikely to survive . While Cristina tries to find an oxygen tank and water for to try and save Lexie, Mark takes Lexie by the hand and professes his love for her, telling her that they were "meant to be". While fantasizing about the future that she and Mark could have had together, Lexie succumbs to her injuries, and dies moments before Meredith arrives . The remaining doctors are left in the woods waiting for rescue, with Mark refusing to let go of Lexie's hand . </P> <P> The remaining surgeons are rescued from the woods days later, and Lexie's body is returned to Seattle . Weeks later, a traumatized Cristina reminisces to Owen Hunt (Kevin McKidd) about her time in the woods, telling him that she had fought with wild animals to keep them away from Lexie's body . Weeks after the crash, Meredith comes across a young girl presenting with injuries identical to Lexie's, and tirelessly works to save the girls life, with the experience eventually causing her to come to terms with her sister's death . Despite making it home from the woods, Mark later died from the injuries he sustained in the crash . When the survivors of the plane crash pool their compensation money to purchase the hospital, they agree to rename the hospital to "Grey Sloan Memorial Hospital" in tribute to Lexie and Mark . </P>

What happened to meredith's sister on grey's anatomy