My intent is to keep you out of trouble by trying to explain a few tax rules in hopes that this might prevent additional problems for you and your partner. Please be aware that a dependency for a child is not something that you are normally free to just move around between people to get more money. (There are some exceptions for if you are divorced/separated under a legal arrangement.) Instead, the IRS has tax laws that define who can claim the child. (I'm assuming that you are not married, and that the mother, your partner, has legal custody for the child, and your partner lived with the child more nights than you did.) In the process of filing her return, your partner would have needed to make legal statements to certify that she is the one who is entitled to the dependency. Your partner needed to state that the child lived with her for over half of the year. And since she filed single, she would have indicated that the child is not a qualifying child of another taxpayer. I assume that her original answers were truthful. So if you now try to change the original story with an amendment, then you might also need to have an explanation ready to explain why her previous statements should be considered truthful at the time they were made. Also, you should be able to defend why any statements on the amended return are the real truth with regard to custody and support of the child. Please understand that the IRS is normally sympathetic to simple mathematical errors. But when the IRS believes one or both of you is making false statements to manipulate credits, then the IRS has power to take some or all of the credits back for this year and to deny them for future years. Bottom line: please be honest so that you do not make matters worse. I wish you both well for your futures.
When both parents live together with the child, then the IRS has tiebreaker rules that define who has the priority to take the deduction. You might win the tiebreaker if you have the higher AGI. The tiebreaker rules are explained at this link:
Yes, it is "possible" to amend your returns. Be aware that if your partner amends, then she will be required to pay back any excess money which she received. I don't believe that it will matter that the money was taken by DOE. Instead, I believe that the IRS will book the money as being returned to her accounts. Do you think that the DOE will agree to send money to you that would increase your debt while your account is already in collections? I can only say that if you choose to amend, then accept the fact that you could be begging for questions and could be taking risks that might not go in your favor. You will need to make your own decision on this. Just don't commit any fraud to manipulate tax credits because that could create a long-term financial problem that you don't need.