Complex sentence: Lisa is shocked by Marge's injustice and confronts Marge for it, but when Marge refuses to stop or acknowledge that she was abusing Bart's privacy, Lisa decides to tell Bart what's going on.
Split into simpler sentences: Lisa is shocked by Marge's injustice and confronts her for it. However, when she refuses to stop or acknowledge that she was abusing Bart's privacy, Lisa decides to tell Bart what's going on.