First, if your daughter files a joint return with her spouse and their income is more than $25,900, or they claim any deductions, credits or dependents except the standard deduction, then you can't claim her as a dependent. Her decision to file jointly will override everything else.
If she files jointly but she and her spouse have less than $25,900 of income, and the only reason they file is to claim a refund of withholding, and they owe no tax and claim no credits, then you can claim your daughter as a dependent if she meets the usual qualifications. Or, if she files as married filing separately, you can claim her as a dependent no matter what her income is, as long as she meets the usual dependent qualifications. In either case, she must answer "yes, someone else can claim me as a dependent."
If she files MFS, then her spouse must also, and this usually results in higher taxes because the MFS rates are different, and many deductions and credits are reduced or disallowed. Most of the time, the spouse will pay more tax filing MFS, than you save by claiming your child. But the only way to know for sure is to try different combinations.
