I was admittedly caught off guard and I didn't know how to respond and just said something like "wouldn't that be nice, but that's up to mommy"
Nope nope nope. Don't put it on your ex and don't give your daughter the idea that this is a possibility, because it's very unlikely to happen and she doesn't need to think it can.
Instead, try to put a positive spin on it. "You have two bedrooms and two blankies" "You have daddy here and Mommy and OM there". Or just factual - mommy already has OM she lives with . (If she does).
You might ask Ginger for her opinion on how to handle this. Despite the fact that her daughter was an infant when her ex split, she also got these questions from her daughter.