It's very unlikely that Molly would get up during labor, and get herself trapped. Generally a queen will stay in the birthing area until she's done birthing, and often won't even leave the litter for a day or two. Don't beat yourself up over it, as a cat will look huge right before the kittens drop into the birth position. They don't look quite as enormous the day of delivery. If she truly seems miserable inside, and has a warm safe place to stay especially during the Winter, then maybe she'd be happier outside again. Have you tried leaving the cage door open to see if she'd be willing to come out? Then there's the other dilemma of her possibly using her hiding spots as a potty.