Yes. While there has been much debate about when to intervene on children with regards to non-nutritive sucking, the age of 12 is decidedly too old to continue the habit. Thumb sucking (or any such repetitive oral behavior) can lead to multiple long term consequences, some of which you may have noticed already. In addition to the spread of disease,increased infections, and the effect on dentition, the chronic force of repetitive thumb sucking can cause alterations in the development of the bony anatomy of the face. At the age of 12, this may have already occurred to some degree.
Rapid intervention at this point will prove critical to avoiding further problems. Additionally, this behavior is likely to become a social issue as well, with teasing from peers obviously taking a role in her personal development. Fortunately, there is much that can be done. Speak to your pediatrician
about the problem. Depending on what you have tried previously, there are multiple options available.
Some of these may even include wearing an oral device that makes it difficult for her to suck her thumb. While it may be difficult in the short term, please speak to your pediatrician soon about this problem.