She's probably just overwhelmed. Two little ones under the age of four, with one an infant, is a huge job. And she probably is justifiably worried about choking hazards with an infant at the stage where she puts everything in her mouth. She's also naturally biased in favor of her own infant and will have to have some time to adjust to having another child in the household that isn't her own birth-child.

Help your girlfriend. Help keep Skyla well guided, no matter how much you want to spoil her and let her do whatever she wants. If she's been through a lot, she likely hasn't had much in the way of structure or boundaries, and kids need those things. And above all, work hard at keeping that relationship together. You have two little children who need two stable, loving, in-residence parents. It wouldn't be fair to you or to either of those babies for one of you to bail out. Good luck!