T.S.
There is this stuff that you can put on her thumb that tastes soooo badly that she won't want to put her thumb in her mouth anymore. My daughter tried to start thumbsucking when she was 2. I put that stuff on her and after she spit, drooled and gagged for a couple of days, she quit. It comes in a clear bottle, not sure what it's called, but you just brush it on her thumb and you should see results soon.