bump under tongue

My 15 year old daughter has been complaining about a small bump that seems to be getting bigger, located where the tongue web meets the jawbone. It's not painful, but feels sore when she applies pressure to it. It moves slightly when pressure is applied, and she's very worried about what it might be. You can't see it at all, but she feels it with her tongue, and I did feel it with my finger. It's about the diameter of a pea, but flattish.

Does anyone know what this might be, or if it's anything to be concerned about? Would we see an MD or a dentist about this?

[Jerome Tsang, DDS]

Probably an oral surgeon.  It sounds like it may be a salivary stone to me.  That's when there's a calcification of the salivary gland duct and it gets blocked and becomes a small pebble like object in the bottom of the mouth.