Complex sentence: When she is about to kill him, the Cheetah appears and kill her aunt, claiming that she was the last piece of Barbara Minevra's past, and with her death, Minerva would die as well.
Split into simpler sentences: When she is about to kill him, Cheetah appears and kills her aunt. Cheetah claims that her aunt was the last piece of Barbara Minevra's past and with her death, Minerva would die as well.