"I am guessing her next move is to move out. Any advice on what to say if she drops that bomb? Trying to be prepared mentally for whatever happens..."

Upper, you won't be ready. Just know that. The only thing you can really prepare for is that it's going to affect you in a way you didn't expect. Unless you are completely, emotionally detached.

Me 47 - W 35
M 9 - T 10
2 Daughters - 7 & 9
Discovery of EA- 8/4/14
S - 8/5/15
D mentioned - 9/11/14
R & Piecing - 3/17/15
Regard one another as more important than yourselves.
- Philippians 2:3