I'd stay. C'mon, OP, if she's not smoking in the house your secondhand exposure is minimal, so it's just about you hating the smell. It's unpleasant, yes, but it's not going to kill you (or your child).
Speaking of smells, I hate the body lotion/perfume my MIL is wearing to the point that it's making me gag; I'm not allergic per se, it's just this particular
scent doesn't sit well with me. Still, we visit, stay in their house and I'm holding my breath when I have to come too close to her. Would love to stay at the hotel, though, but don't.