I wouldn't worry either. As Olive said, how do you stop a baby from doing that? If it settles her then why try to fix something that isn't broken, IYKWIM. She may just outgrow it eventually, a lot of kids do. I sucked my thumb until I was 10 ( yes, I know) and my palate is just fine. I did need quite a bit of orthodontic work in my teens but it is unusual for a child to suck their thumb for that long. I was a complete addict!

They say dummies can be bad for their teeth/palate (hence the orthodontic dummies) so I don't think you can win really! I say let her comfort suck her fingers, I personally think it's adorable