Are you talking about adultery? Personally I don't think I can tell anyone that is what they are doing is wrong, cause I'm no better. I would certainly pray for them, and definitely listen to them. Dont encourage them either.
Just know, we have a just, fair God who will be her judge, along with the Elect.
You ever consider sharing with her what you have been learning here?
2Ti 2:24 And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient,
2Ti 2:25 In meekness instructing those that oppose themselves; if God peradventure will give them repentance to the acknowledging of the truth;
2Ti 2:26 And that they may recover themselves out of the snare of the devil, who are taken captive by him at his will.
I dont know, but just maybe if you share with her some Scripture or something from Rays teaching, and that your learning, maybe she will get the hint that it makes you uncomfortable, if that is what the REAL problem is.
You know you really cant change anyone? That is up to God.
Thats a tough one for sure, maybe someone here can give better advice.
Praying for your wisdom in this matter.
Peace, G.Driggs