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

From your description and the photo, this could be a large blood blister from pressure or unnoticed trauma, but the size, color, and pain also raise concern for infection or a severe reaction. Do NOT pop or cut it at home. That can introduce bacteria, worsen a hidden infection, and make walking even more painful.

Check gently: is the area soft and squishy like a fluid-filled blister, or firm, hot, and very tender even to light touch? If it’s hard, hot, rapidly swelling, streaky, your child has fever, or refuses to bear any weight, go to urgent care or the ER today. If it’s soft, not rapidly spreading, and your child is otherwise well, you can still call your pediatrician or an urgent care now for same-day evaluation and pain relief, so they can safely drain or treat it and stop the swelling and pain.