If your girl friend, then YOU could not claim her. (If you were married at the end of 2019 then you should have filed jointly).
If not married and she did not live with her father more then half of 2019 (unless she was under age 24 and a full time student temporary away to attend school) then he probably should not have claimed her, but that is between him and the IRS.
There are other options depending on the circumstances but you did not provide the details.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
