here is the IRS work schedule to determine "support"
https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
note that the IRS considers her living at home, even if she is living in a dorm / off campus apartment. So for example, if you are a 4 member family, then 25% of the housing expenses would be allocated to her on this worksheet as support you provide; that makes it very difficult for her to provide 50% on her side. Estimate some of the items as you'll begin to prove the case that you provide more than 50% of her support.
for college, did she not sign the forms when she entered college to give you access to her grades and financial information? this is a tax forum, but who is paying the college tuition? maybe it needs to be held hostage in return for access to the financial information.
note the the tax return asks if she CAN be claimed as a dependent not if she is claimed as a dependent.
good luck!
