I think you first have to decide, Is the contact she's having with this person a dealbreaker for you?
It's a bit like being married to someone whose alcohol consumption is a problem for you but it isn't for them. You get to decide what's a problem for you.
Me 57/H 58 M36 S 2.5yrs R 12/13
Let me give up the need to know why things happen as they do. I will never know and constant wondering is constant suffering. Caroline Myss