If she qualifies as your dependent you can claim her but you will have to print and mail your return if your ex already claimed her. Then the IRS will investigate to determine who can claim her.
If you don't claim her you can try to efile until Oct. 15, 2021. After Oct 15 you will have to print and mail returns. If you are getting a refund you have 3 years to file to claim it.
If you are using the Online version, Online will shut down soon after Oct. 15, 2021. So finish and file by then or you will have to switch to the Desktop program.
