She can NOT file without being a dependent this year.
There is a rule that says IF somebody else CAN claim him/her as a dependent, he is not allowed to claim himself. If he has sufficient income (usually more than $12,400), he can & should still file taxes. In TurboTax, he indicates that somebody else can claim him as a dependent, at the personal information section. TT will check that box on form 1040.
Even if he had less, he is allowed to file if he needs to get back income tax withholding. He cannot get back social security or Medicare tax withholding.
Technically, it is not the father that CAN claim her, even though you have an agreement with him to allow that. You are the only person who can claim her. There is a special rule that allows divorced and separated parents to split the tax benefits up until the age of emancipation. Since she is 20, the father can no longer claim her, since she lives with you (unless you live in Mississippi).
There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.
A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:
- He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
- He did not provide more than 1/2 his own support. Scholarships are excluded from the support calculation
- He lived with the parent (including temporary absences such as away at school) for more than half the year
Under the CARES Act, if you are claimed, or qualify to be claimed, as a dependent on someone else’s 2019 return you cannot receive a stimulus check, in 2020. If you qualified as a dependent for 2019, but will not be for 2020, you will most likely get it in 2021, when you file a 2020 tax return.
Note that the requirement is not just whether you are actually claimed as a dependent, it's whether you qualify to be claimed as a dependent.
