If your college student claims her child and the Earned Income Credit (EIC), you cannot likely claim her as a dependent.
These rules generally apply to all dependents:
- A dependent must be a U.S. citizen, resident alien or national or a resident of Canada or Mexico
- A person can't be claimed as a dependent on more than one tax return, with rare exceptions
- A dependent can't claim a dependent on their own tax return
- You can't claim your spouse as a dependent if you file jointly
- A dependent must be a qualifying child or qualifying relative
See IRS article here.