M.S.
Honestly, I wouldn't worry about it much at this point. Once she transitions to a cup (at around 12 months), that would be a good time to start trying to break that habit. We waited too long and it took forever. The way we finally got it done was we bought some yucky tasting stop-thumb-sucking nail polish (found it at Wal-Mart) and that did the trick almost over night. As for right now, sucking her thumb is just soothing to her and she isn't old enough to understand how to soothe outside her own world. Children this young are self-involved and don't know just how to use their world for self-comfort. It won't impact her speech or her teeth at this time, and, as for the shape of her mouth, it would only impact that if she constantly sucked her thumb. If you would like some info, go to www.superduperinc.com. They have parent fact sheets and they have book dealing with this very subject. Best of luck to you!