Yes, even though many schools pledge to meet 100% of financial need, there are often incidentals that might not be covered - like travel to and from the university (not incidental if you are flying from the East Coast to the West Coast and back twice a year), books, spending money, etc. I know that nominally those are covered by the cost of attendance, but unless this school is giving you a stipend to cover those things - which is uncommon - or you have work-study or employment that will cover it, you will need minimal support from your grandmother if you can get it.
That said, I agree with @happymomof1 - if you can get a trusted adult to be your advocate in this case, that would be the ideal way to go about this. They can have an adult-style heart-to-heart with your grandmother and have the bonus of appearing to be a neutral third party.