There are two different types of dependents with different rules, and your daughter might qualify for either one.
For qualifying child dependent, the child must:
1. live in your home more than half the year
2. not provide more than half their own support
3. be permanently disabled.
For IRS purposes, disabled means unable to perform gainful work, due to a condition that is permanent or will last at least one year. The gainful work rule means that many people with medical disabilities, but who can still work a regular job, are not considered disabled for tax purposes. Work in a sheltered workshop is not considered gainful work, but the ability to work at least minimum wage job is generally proof that a person can perform gainful work, even if some accommodations are needed. I wonder if there are legitimate work-from-home jobs your daughter might be able to perform, especially with so much more work from home now than before the pandemic. That will depend on her medical condition of course. If your child is unable to perform any gainful work, and a doctor can certify the condition will last at least a year, then your child can be your qualifying child dependent.
For the support test, it is not necessary that you prove you provide more than half her support, only that she did not provide more than half her own support.
Or, there is the qualifying relative test. To be a qualifying relative dependent, your daughter,
1. does not have to live at home
2. you must provide more than half her support (this is a different support test than for qualifying child)
3. she must have less than $4300 of taxable income in her own name (job, investments, and so on).
