The first thing I thought of was did the puppy lick her? I can't see your signature with this posting window open, but I noticed that you listed a new puppy, and I wondered about treats & food that they might have eaten, been exposed to, or might be on them. Even the smallest little lick to a cheek, or to hands ... that seem harmless and just part of living with a puppy.... can end up with hives & reactions.
If your DD is in the habit of washing hands when she gets home, and had a reaction, but was only eating things she has already eaten before with no problem, then I would probably look to the puppy first (if I were sleuthing). Not that they are bad or anything. We had a couple reactions happen when our now 10 year old dog was a puppy..... from her licking.