There is no stimulus for tax year 2019. She gets the 2020 and 2021 as long as she did not qualify as someone else's dependent. She claims the stimulus by filing tax returns for those years (the IRS may actually send her the 2021 advance stimulus after she file her 2020 tax return).
So your other question is: does she qualify as your dependent. Support ("I am paying for all her expenses") is only one of the dependent tests.
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). She is too old to be a QC.
A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:
- Closely Related OR live with the taxpayer ALL year
- His/her gross taxable income for the year must be less than $4300 (2020).
- The taxpayer must have provided more than 1/2 his support
- He must be a US citizen or resident of the US, Canada or Mexico
- He must not file a joint return with his spouse or be claiming a dependent of his own
- He must not be the qualifying child of another taxpayer
