my 20 year old daughter did not work last year due to brain tumor, cancer, why can I not claim her as a dependent..I supported her for a year

[xmasbaby0]

You can claim your daughter as a qualifying relative dependent if she had less than $5050 of income during 2024--not counting Social Security.   You will get the $500 credit for other dependents and if you are itemizing deductions, enter any medical expenses you paid out of pocket for her care.

Qualifying relative

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year (exceptions apply).
• They made less than $5050 in 2024.   (Not counting Social Security)
• You provided more than half of their financial support.

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them. There may be other tax benefits you can get when you claim a dependent.

Related Information:

• What does "financially support another person" mean?

[MinhT1]

I assumed that she is not a full-time student.

If you paid more than half of her support and she earned less than $5,050 in 2004, you can claim her as a dependent (qualified relative).

Please read this TurboTax article on Who Can I Claim as a Tax dependent?