The problem is that only one taxpayer can claim the child as a dependent. If you want that to be you for 2015, then your GF needs to file amended returns to remove the child. You will want to start with her transcript for 2015 as well to make sure she did claim the dependent and that the IRS did not already adjust her return. If she did claim the dependent but you want to be the person who does, then she needs to file amended federal and state returns and that needs to be part of your answer to Ohio when you work on this issue with them.
