I think you are way too smart for this. You might be conflicted. Wanting to lend your sister an ear, but not wanting to hear inappropriate info./too much information/and info that crosses a boundary. Like Kathy mentioned, if it crosses a boundary, it doesn't matter who it is with. And you have every right to state that you don't wish to hear this info and if she doesn't respect this, that is very inappropriate. Although therapists can be costly, it might be time for your sister to have some sessions with a therapist to get some of this stuff "processed" in a safe environment. It is a complicated and confusing time for her and other's involved and people's feelings could easily be hurt. Good of you to consider the sensitivities here.
