Don't give advice to her, but be willing to help her see the pros and cons of dating someone that much older at this time in her life. That age difference is huge at this point. In another 3 or 4 years, the age difference is negligible. But freshman and senior...huge.
I think young people need to make their own decisions, but helping them clearly see the possible consequences of their choices is a noble thing. Just make sure she understands it is her call to make.