Childhood sucks

Well, to be more specific, my daughter sucks... her thumb. Since I don't know of any adults who suck their thumb, I figured she'd probably kick the habit at some point. Sadly, just went to see the dentist who says she's concerned about my daughter's upper pallate and her front teeth. I've talked to her about it, and she's trying to quit, but the thought of quitting makes her upset, and when she's upset, she sucks her thumb, so it's a bit of a sick-sucking-cycle.

Anyone out there have thoughts that don't end in hysterical sobbing? Something that my daughter could try would be good too.