H.J.
C.,
Wow, 12 huh? that's a harder one, they are smart enough to know how to get around all teh tricks we try on our babies... I guess you almost get to the level of does she want to quit? You said you have tried gloves and bad tasting stuff, have you tried athletic tape? it's harder to get off and you could wrap both thumbs at night... (just a thought I have no idea if that would work)
My best friend had an orthodontic apperatis put in her mouth, it looked pretty midevil, but it basicaly went on the roof of her mouth and made it very uncomfortable to suck her thumb. Perhaps you could inquire into something like that..
I toothought we were going to have this battle since my daughter was a thumb sucker, unfortunatly when she was 2 she burned her whole hand on our stove with 2nd degree burns and was unable to suck her thumb through the inch of gauss wrapped around her thumb,(it was awful) afer 3 weeks she was over it.... So I can tell you that it should take about 3 weeks or so to break the habit, perhaps longer....
Good luck..
H.