E.A.
I don't have any advice but I did some googling for you:
1.from http://www.drgreene.com/21_10.html
"When investigators looked at this group of late thumb-suckers for common traits, they found that they had one thing in common that distinguished them from other children -- a prolonged history of a strong battle with thumb sucking at an earlier age. It is striking that many well-meaning parents have actually encouraged this behavior by trying to forcibly take the thumb out of their children's mouths."
2.here they suggest dental appliances
http://www.drugs.com/enc/thumbsucking.html
3.but basically most sites suggest the following
(this is from http://www.wrongdiagnosis.com/t/thumb_sucking/intro.htm)
Watchful waiting - most cases require no treatment.
Psychological treatment - if the habit is used excessively or the cause is an underlying psychological problem.
Dental treatments - if dental complications occur.
Finally, you might want to watch the movie Thumbsucker. I don't think it's completely appropriate for a 9yo, but if you think it is, she can watch it, too. Yes, it's fiction, but I was impressed with how they handled the issue. I had friends in college who still sucked their thumbs, and although they got teased for it, they all turned out ok.