The fact that she already filed doesn't mean you can't claim her. It's not a case of whoever gets there first wins. She meets the qualifications except for possibly one below. She did something with her money. What was it. Even if you provided the stable things like home and food, whatever she spent it on probably also went towards support.
Support — did not provide more than one-half of his/her own support for the year.
For the purposes of the Head of Household filing status, a qualifying person is a child, parent, or relative who meets certain conditions, listed below.
The conditions are stricter than those for claiming a dependent; for example, you might be able to claim a roommate as your dependent, but never as a qualifying person for Head of Household status.
A qualifying child would be:
- Your child (including legally adopted), stepchild, foster child, sibling, half-sibling, step-sibling, or a descendant of any of them (for example, your grandchild or niece) AND
- Permanently and totally disabled OR under the age of 19 as of December 31, 2020 (under 24 if a full-time student) and younger than you (or your spouse, if filing jointly) AND
- Lived with you for more than half the year AND
- Single (or if the child is married, you'd have to qualify to claim them as a dependent even if you're not going to claim them as such).
A child that is too old to qualify as a child might be able to qualify as a relative for Head of Household. A qualifying relative would be:
- Your mother or father (including your stepfather or stepmother), if you're qualified to claim them as a dependent (even if you're not claiming them as such) OR
- A relative related by blood, legal adoption, or marriage other than a parent (see the full list of qualifying relatives below) AND lived with you for more than half the year AND that you're able to claim as a dependent (even if you're not claiming them as such).
- Qualifying relatives:
- Your brother, sister, half brother, half sister, stepbrother, or stepsister.
- Your grandparent, or other direct ancestor, but not foster parent.
- A son or daughter of your brother or sister.
- A son or daughter of your half brother or half sister.
- A brother or sister of your father or mother. Your son-in-law, daughter-in-law, father-in-law, mother-in-law, brother-in-law, or sister-in-law.
