Sore Inside Cheek My Mom Just Found This Black Sore On The Inside Of Her Cheek?

My mom just found this black sore on the inside of her cheek? - sore inside cheek

Out of nowhere, she felt something strange in the mouth, and when I asked to see it, we realized it was a black pain. Apparently, so after eating. It does not hurt or feel tender only strange thing to have a light bulb in his mouth. No idea why, and whether or not it dangerous?

Thank you very much!