She just did. It wasn't a big piece I don't think. She was outside and I think she was just licking it and when I came out she swallowed like a 2x2 inch piece. What should do?

I would keep an eye on her. It may pass without harm. If she shows any signs of digestive upsets, vomiting, diarrhea, or constipation, call the vet.

Also watch for black or bloody stools too. The foil may have cut something on the way through

55 lb dog ate aluminum foil that had olive oil and fish drippings. Anything to do tonight?