Nothing is ever inevitable. It will undoubtably take a lot of talking and negotiating, but there's no reason everything else can't be salvaged. It sounds like you're ending on relatively good terms.
If AA moves out, that's her choice. Three people in a one bedroom, it's no wonder there are issues. Her moving out, alone, could be something that helps your relationship. You say she's still there because of financial reasons, which leads me to wonder if it was financial reasons that got her living there in the first place. That rarely works out well as a permanent solution.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker