I have to disagree with what was suggested above. If you can prove that you're the tenant, and that the roommate is your subtenant, you can proceed to evict your subtenant. It would be sensible for you to have grandma execute whatever documentation you believe may be helpful in court, in the event that your standing to evict is challenged.

You have told us nothing about the lease, save that it's term expired six months ago. Some leases end at the conclusion of the term, some automatically renew for a fixed term, some automatically become month-to-month leases on the same terms. If the lease is silent on what happens after the initial term, or provides that it continues on a month-to-month basis, then you can modify the lease upon proper notice and can also give notice to quit. If it renewed for a specific term, then you will need to give proper notice to end or modify the lease before it next renews.

I am not clear about whether your lease provides that the rent includes the amount you are trying to charge for utilities, or if you are trying to charge an additional amount despite there being nothing in the lease about an additional payment for utilities above and beyond the rent. It makes a big difference. If the lease does not require an additional payment for utilities, then you almost certainly have no right to collect even a penny toward utilities.