Yeah, breeder traps (Or what you call fry holders) are not big enough for large fish like Mollies. They should really only be used for smaller fish like Guppies, maybe Platies. Or once they have started giving birth. If you haven't taken her out yet, I would. Otherwise, it could stress her out very much to be in there, which could lead to birthing difficulties, abortion, or even death. If you want a way to save the fry, either plant up and decorate the tank very well to give them hiding places, or get a breeder net and transfer the fry into there to raise them for a few months. There is a post pinned in this forum about Breeder traps and nets, you may want to read that.