Answer by taking a quote from the following article:

Psylocke (Elizabeth "Betsy" Braddock) is a fictional superheroine appearing in American comic books published by Marvel Comics, commonly in association with the X-Men. Created by writer Chris Claremont and artist Herb Trimpe in 1976, she first appeared in the Marvel UK series Captain Britain. Betsy was initially a supporting character in the adventures of her twin brother, Captain Britain, even briefly substituting for him in the role, before becoming the mutant superheroine and X-Men member Psylocke in 1986. Originally presented as a precognitive in the pages of Captain Britain and then as a telepath, the character eventually had her mind placed in the body of a Japanese female ninja known as Kwannon, gaining many of Kwannon's martial arts skills and elements of her personality.

One year after her death, Betsy awoke where she had died, unaware of how she had survived, and was soon reunited with the X-Men, helping them against the Saurian Hauk'ka, and Mojo and Spiral. Jamie started to covertly observe his resurrected sister, allowing her to catch occasional glimpses of him. Betsy was reunited with Brian during the Scarlet Witch's "House of M" reality storm. When the timeline was set right, the memories of their encounter took on a dreamlike state, prompting Betsy and several of the X-Men to visit London to check on Brian's status. Back in the USA, Betsy and the X-Men failed to stop Shi'ar Death Commandos from slaughtering the Grey family, targeted for death because of their relationship to Phoenix, but helped defeat them before they could kill Rachel Grey. With the First Fallen's servants, the Foursaken, about to make their move, Jamie revealed his part in Betsy's resurrection to the X-Men: sensing the approaching threat of the cosmically powerful First Fallen (a harbinger of frozen, eternal "perfection") and learning of Betsy's demise, an annoyed Jamie resurrected her, reaching back through time to stop her spirit passing into the afterlife. Intending her to be a weapon to use against the First Fallen, Jamie tightened up the "quantum strings" of Betsy's body, rendering her mostly immune to external manipulation, enhancing her telekinetic powers, and leaving her invisible to the First Fallen's senses. Jamie was abducted by the Foursaken before he could fully inform them of the imminent threat; trying to rescue him, the X-Men were easily captured, except Betsy, who found herself invisible to the Foursaken's senses. Disrupting their attempt to give the First Fallen full access to Earth, Betsy and the X-Men were pulled into his realm, the Singing City, where Betsy's immunity to his mental control allowed her to free the City's residents, including the Foursaken, from his dominance. As a wrathful First Fallen turned on them, Jamie sent the X-Men home while he held the entity back, apparently sacrificing himself. Returning to the UK to tell Brian of Jamie's fate, Betsy learned that Shadow Xavier, leader of the Shadow X-Men, had taken over the minds of his jailors in Crossmore Prison, and was demanding to see her. Accompanied by Excalibur, Betsy visited the prison, where Xavier revealed his true identity as the Shadow King, and tried to take revenge, having Excalibur attack Brian so that Betsy could witness his death; however, immune to his control, Betsy telekinetically induced a stroke in Xavier's body, freeing Excalibur. Before she could finish him off, Psylocke was interdimensionally teleported to the Crystal Palace at the Nexus of All Realities. CANNOTANSWER

how did she die?

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