Can my ex amend her tax returns to claim child tax credits that were originally agreed to go to me?

My ex girlfriend lived with me for 9 years as unmarried cohabitating domestic partners. We have an 8 year old daughter together. We lived together as a family under the agreement she pay me a monthly amount towards living expenses (she called it "rent" on the checks), and I claim our daughter on taxes... show more My ex girlfriend lived with me for 9 years as unmarried cohabitating domestic partners. We have an 8 year old daughter together.

We lived together as a family under the agreement she pay me a monthly amount towards living expenses (she called it "rent" on the checks), and I claim our daughter on taxes every year, which made sense since I paid the majority of our child's expenses.

After we broke up and she moved out, she visited an accountant who amended several of her previous tax returns, giving her a tax refund for several years of child tax credits. Meaning the IRS will now go after me to try to get back the child tax credit money which I already claimed DUE TO THE AGREEMENT I HAD WITH THE MOTHER AT THE TIME I FILED.

Is her accountant legally liable for any damages by advising and filing her amendments that unjustly claim the tax credits that were already agreed to me years ago?
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