My daughter woke up with this huge spot on her foot I don’t know what it could be. She’s been in pain and can’t move her foot what is this..

I’m really glad you shared the photo — this looks serious and painful, especially for a child .From what I can see, it looks very similar to a blood blister (a blister filled with blood instead of clear fluid). These can become large and dark when pressure or trauma happens while sleeping (for example from tight shoes the day before, friction, or a small injury that wasn’t noticed).