Thanks Ovr and Joe for your comments.

Well, I have already confronted her and she moved out late April'2019. So, she knows that I know of the OM.
Don't know why she keeps lying and making excuses. Feels more cheated than the actual affair.
I had told her during confrontation that I know of the affair and not ready to live in an open marriage. She had planned to move out and she did in April. During initial days after BD, she had mentioned that she wanted to move out because she wanted to gain her self confidence and didn't want to live in the hose she had bad memories in and hated being with me.
Later I discovered that it was not just about that but more about having a free go at being with the OM with no restrictions.

Should I be telling her that I will keep our D and I know what actually she is going to do during that weekend instead of the meeting she is telling me about?
What is that going to get me? She knows I know about the OM and this may prove that I am not over her and still want to control the situation, which I honestly don't want. I just feel said that this girl who never lied to me for 10 years, now lies to me every day or I should say with every communication she makes with me and that is heart breaking.

I was thinking that I should just message her "Yes, I will keep the daughter."

Thanks!