My 7 year old daughter's friend just quit sucking her thumb about 4 months ago (she's 8 years old). Here's what they did after trying all the other ideas (no-bite nail enamel, tabasco, etc) First, since she was old enough and aware enough they spoke to her about thumb-sucking...the stigma, the security it provides and the actual physical habit. They asked her if she had any ideas to help her stop too. She seemed excited that she was being involved in the decisions (instead of being told or forced to stop!) The tongue is an muscle and needs to be trained (some people are tongue thrusters) so most dentists will recommend training the tongue to curb tongue thrusting and yes, even thumb sucking! It worked for our little friend by using hard candies...you place one at the roof of the mouth and hold it there with your tongue. Yes, this may take time but any solution will. There are many different sugar-free candies out there too, I'm sure you can find one your daughter likes. Hope this helps!!! Good luck (just remember to encourage her, dont be negative or stigmatize her for it!)