Advice has gone up w/ inflation; so here's my 5 cents
I agree that SHE might not be "doing anything" b/c she's got the "heeby-jeebies" BUT considering she's horning in on your father, I PERSONALLY think she ain't hauling her load of this "relationship" Why not tell your DAD talk to HER & stop making you play the go-between?
Dottie's right, we all chose our own personal friends w/ our hearts -- not d/t "future family conveinence" (sorry, if I misquoted you too bad Dottie!

)
Been there,