Your daughter is not declaring on her tax return that "she is claimed as a dependent." She is declaring that she can be claimed as a dependent. You cannot choose whether or not she can be claimed. If she meets the requirements that DoninGA listed, you can claim her as a dependent and she has to say on her tax return that she can be claimed, whether or not you actually do claim her.
If you can claim her, you might as well do so. It will not affect her tax return because she has to say she can be claimed, whether or not you actually claim her, and you will get a credit on your tax return for claiming her.
If she does not meet the requirements for you to claim her as a dependent, there is also no choice. You cannot claim her, and she will not indicate on her tax return that she can be claimed as a dependent.
You can use the tool at the following link on the IRS web site to determine whether or not you can claim your daughter as a dependent. It covers all the criteria that might apply.
Whom may I claim as a dependent?
