even though she is 19, you may be able to claim her as a dependent (qualifying child or relative) for 2020
you can claim her as a qualifying child if all these tests are met
• she has the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored
• if she is not a full-time student, she's under 19 at the end of the tax year. If a full-time student, she's under 24 at the end of the tax year.
• she hasn't provided over ½ his own support
• she didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate refund of taxes withheld or estimates paid
or you can claim her as a qualifying relative if all these tests are met
• her gross income for 2020 less than $4,300
• you provided over ½ her support
• she isn't a qualifying child of another taxpayer
while you don't have to claim her if she qualifies, if she is your qualifying child or relative. regardless, she must indicate she's can be claimed as a dependent on another's return.
if you can't claim her then you will have to file an amended return after your original return is fully processed. since it would seem you filed first, she will now have to mail in her return because her SSN has been used on a return that has already been filed
