I tried to look at Carolina's FB. It is odd, and I couldn't figure out the timings. The last few posts seem so focused on the new baby, happy family pictures. Someone suggested earlier in the thread that Carolina's job(s) might mean a lot of people knew she was pregnant and had a new baby, but those FB pictures and no reported break-in makes me wonder if Carolina knew this woman, maybe even FB friends with her. A woman in that state of mind seeing those lovely family photos...it's going to be a stressor.
I don't know if I'm allowed to say this, but I would look for friends of Carolina, at least people she knew enough to let them into the home, maybe a distant relative, probably someone in the community she belonged to, presumably someone who could pass off this baby as their own, so possibly similar racial background or at least has a partner who could pass as the father of this baby, and maybe even someone who saw those FB pictures. The settings were public, so anyone who liked those pictures, it would have shown up in the side bar for one of their friends, but at the same time I think someone who knows Carolina enough to know where she lives and to knock on the door and say "Hi, I've come to bring a present for the baby and sit and have a coffee with you".