Yes you can still claim her even if he did. Did you file 2020 without her? You can amend 2020 to add her. Don't worry about what he did. File your return right and claim her. If your efile rejects because he already filed you can print and mail your return. The IRS will sort it out.
How to Amend all years
https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...
