Since you effectively claimed yourself, not as a dependent, but as a tax filer (taxpayer), no one else can claim you as a dependent. If someone else did so (they would have had to mail in a paper return), Down the road (longer than usual this year) the IRS will match the two competing returns. You'll be getting a letter from the IRS and so will the other party. Follow the instructions.
It doesn't make sense that it was your ex. It would make more sense for her to try to claim your daughter.
