You will have to print and mail your return to get it accepted. If you are right and her mother mistakenly filed as the custodial parent, she should file an amended return to change the way she claimed your daughter. If she doesn't, later in the year the IRS will send both of you requests for documentation to prove you were the custodial parent. Whoever wins gets to keep their tax benefits. Whoever loses gets to repay the benefits they should not have received with penalties and interest.
