Reasons for a white bump in your mouth?

So for about a month there’s been this white bump near her bottom right (her right) molar that’s about the size of a dull pencil tip.

Doesn’t hurt as far as we know but we can’t touch it due to her gag reflex.

She’s going to se a doctor within the week, but she’s flipping out about oral cancer right now. I just think it’s a very sturdy cold sore but I could be wrong. Any ideas what it is so I can sooth her a tad?