That's a hard situation. It does sound like the mare might have taken her but there's no way to know, hopefully she did and she got some colostrum. You did need to get her warmed up or you could have lost her too, good for you for reacting even if it didn't go as planned. It is not normal for the mare to have left her alone. If it happens again, and hopefully won't, try using an old sweatshirt as a baby blanket. Head through the head hole, front legs through the arm holes, cut off any extra and use a piece of rope or tape to close it around the belly IN FRONT of the umbilicus. It's probably been too long but you can try taking her out to the paddock and see if her being around without any pressure might get the mare interested again, maybe if you can separate the mare from the herd. That could go bad though so you have to play it by ear. I would probably raise her as a bottle baby and be safe but I'm not there and don't see what you do. Calves from what I know only need to eat a few times a day and eat quite a lot, foals eat little and often, sorry. Goats milk is a good substitute for foals, I don't know if the colostrum will do her any good but it won't hurt. Can you get powdered milk replacer? Foallac. Most feed stores should have it. With not knowing if she got any colostrum, can you take her to the vet for an IGg? It's a snap blood test that will tell you if her immune system is up and running or not. If it is you can work right away on getting her around other horses so she knows she's not a human and more importantly not have to worry about her so much. If her IGg is low your vet can do a plasma transfusion or you can wait it out for the month. You want to keep a really close eye on her this first month. If you notice her a little quieter than normal, not eating quite as much, a slightly swollen joint, swelling around her umbilicus, these are all red alerts that she is septic(sick) and you have to act NOW. Take her to the vet immediately, it's an emergency. Not trying to scare you, I've know some that were rejected and never had a problem, you just have to be aware.
I'm sure there's more to tell you I'm just not coming up with it right now. I hope that makes sense and helps some. Please don't hesitate to ask any questions. Good luck!!