Need Help & Advice; 3yr old will not stop sucking her thumb!

Need Help & Advice; 3yr old will not stop sucking her thumb! She's been doing since she was 4mothns old. This is becoming an issue with her teeth & her thumb as it looks terrible. And her breath is also beeing affected. I've tried band aids, yawky nail polish and even telling her the poor sad looking thumb might fall

​Off. I know that could traumatizing  but she said she had other fingers & she will Be fine! She obviously has no mindset of stopping & I have no clue what to do. Help!