so while i was surprised that mae is already like 'y'know what, i'm good actually' about killing the remaining two jedi (not that i can blame her! i too would not want to kill a wookie w/o a weapon), it also makes sense.
mae's obsessed with osha. it's giving cassandra nova with professor x, specifically as to how for mae, the only other 'real' person in the galaxy is osha. no one else exists. their family, their coven, is long dead. nothing else matters. mae will have her sister in any way that she can - something that she felt so strongly that even as a child, she was prepared to kill osha so she couldn't leave her.
so now that mae knows osha is alive, osha is all that matters - being with her, being near her, being one with her - that's all she cares about. the sith, the jedi, none of that is real.
and it's a fun twist! usually when the villain decides not to continue doing their villain tasks, it's because the main character redeemed them - or that they made a choice to atone. but for mae, it doesn't have anything to do with good or evil. she isn't choosing to become better - by no longer pursuing the jedi, she's actually doubling down on her violent, possessive obsession with her sister. this isn't anakin deciding to save luke and betray the emperor - mae isn't trying to save osha or anyone else really from her master. it's about control - it's about picking back up where they left off when they were children.
it's just osha and mae. mae and osha. always one, but born as two.