Who killed Supergirl in the comics?

Supergirl definitely died, Kara Zor-El story came to an end in Crisis on Infinite Earths #7 (October 1985), in one of the 12-issues of the limited series. Supergirl, in one of the most memorable moments of the series, as she bravely sacrifices her life heroically to save her cousin, Superman and the multiverse, during a cosmic battle against an unstoppable evil. Her death was mourned through the DC Universe for several months, before all of reality came to an end, clearing the way for DC Comics' complete reboot of continuity in 1986.

When DC continuity was rebooted following the Crisis on Infinite Earths, DC editorial felt that Superman should be the sole Survivor of Krypton. Kara was thus erased from the new history of the DC universe.

hell no she was did you not see justice league unlmtied super girl si alvie kara is fine noe eased or dead she go in to future alone super man dos not go with her he stay in the passed she desde to stay in the future she cant give up her life for super man when ther ei sno super man in the future justice league unlmtied was made long after 1985 it wa sin 00 years and super amien siere super girl si alive in that to it in the 00 to so this fake thign was elaserd