First note, even if she lived there more than half the year, she can't legally be claimed as a dependent unless she also:
a. was under age 19, or
b. was under age 24 while also being a full-time student, or
c. was any age but her parents provided more than half her financial support for the whole year AND she has less than $4300 of taxable income.
Second note, if she chooses to file a joint return, that overrides the parents' ability to claim her as a dependent, even if she otherwise qualifies to be claimed as a dependent. In that case, you will have to file by mail.
Or, you can file 2 returns as married filing separately. You only report your income and deductions on your return and she reports her income and deductions on her return. On her separate return, she would check the box for "I can be claimed as a dependent by someone else." Whether this helps or hurts you financially would have to be tested.
