First of all, changing dependent status on a whim is not allowed. If your daughter meets the qualifications to be claimed as a dependent, she must check the box that says "I can be claimed as a dependent" even if she does not want to be claimed, and even if you agree to not claim her.
Second, there is very little tax benefit for her to answering "no, I can't be claimed as a dependent" except for certain education credits, and possibly some health insurance related items. It may change college financial aid calculations, but that is not a tax issue. However, if your daughter can be claimed by you, and she answers that she can't be claimed, and receives a financial benefit, that could be considered tax fraud. Please use caution.
Finally, as stated, amending your return does not remove the block on her account, the IRS just doesn't update that fast. She will still have to file by mail.
