you can her as a qualifying relative (dependent) if all these tests are met
1) her gross income for 2021 is less than $4,300
2) you provide over ½ of her support
if her mother claimed her you will need to paper file
you can also go back and amend 2020 to claim her if
1) her gross income limit is less than $4300
2) you provide over ½ of her support
you can also go back and amend 2019 to claim her if
1) her gross income limit is less than $4200
2) you provide over ½ of her support
3) she is not a qualifying child (QC) of either of her parents.
for her to be QC of either parent that parent must meet all these tests
1) she had the same principal abode as the parent for more than ½ the tax year. Temporary absences are ignored
2) If 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 end of the tax year.
3) Hasn’t provided over ½ her own support
4 Hasn’t filed a joint return – unless there is no tax liability
