if your mil bothers you that much, when she starts "staging" those kinds of conversations with questions, just say "you know, i'm just going to wait and see what happens to work best for us."
that way, you can end the discussion with that, you aren't lying, you aren't being rude. and when you use that exact wording with every one of her "questions," she'll remember and will get the picture. as long as you say it nicely, she can't accuse you of being anything other than a respectful dil who just hasn't made up her mind yet about diapering, feeding, sleeping, vaccinating, disciplining, childcare, college ...
"Dogs stink too, but I like dog stink." ~ rileyb