J.L.
I also have a 2 year old thumb sucker and a 10 month old thumb sucker and I sucked my thumb until I was 8,( only to sleep and only when I was at home). I asked their pediatrician and she said they will stop in their own time and won't suck it at school because other children will tease them. She also said that the "buck teeth" is a myth. Which I know to be true because I have no problem with my teeth.
I have had relatives try to take their thumb out of their mouth and lecture me about thumb sucking, and I hate that. I personally would rather see their thumb in their mouth than a binky. Maybe because I sucked my thumb and I turned out normal..... I would let her be...I am..
My parents tried the chili on the thumb and telling me it would fall off too. I think that is more tramatic than the remote possibilities of dental problems....