as an aside only one of you is allowed to claim her.  just because she did first doen't mean that under the tax law she is not entitled

If your daughter meets all of the requirements to be claimed as a dependent on your tax return, and claimed herself, she will need to amend her return and change her answer to the question that asks if she can be claimed by someone else as a dependent. the rules excluding one that she already meets (relationship) :

1) Must have the same residence for more than half the year. (temporary absences like away at school are ignored) 

2) Must be under age 19 or under 24 and a full-time student for at least 5 months. age doesn't matter if they are totally and permanently disabled.

3) Must not have provided more than half of their own support during the year.

4) The child cannot file a joint return with the exception that a joint return is filed where no tax liability and merely filing to get back taxes withheld. 

 so if all 4 tests are met you get her.