I am an RN with a "home office" three hours away by car. On occasion, we need to go to the office for inservices. The company now said that unless we see a patient before arriving, we will not get paid mileage? This would force me to start work at 6am-working that day at least 10 hours-with no time alloted for a break. I do not believe I am exempt as any work after 4:30pm goes to an on-call staff or has a different pay scale. It seems like the company wants it both ways-Can they force me to do this????

Reimbursement of business related expenses is not required by law at all. So, if the employer wants to set criteria under which mileage will be paid, they may do so.

If you are asking whether this trip can be required, the answer is yes. If you are asking whether you can be required to work more than 8 hours in a day (inclusive of certain travel which may or may not be compensable time), the answer is yes.

I do not believe I am exempt as any work after 4:30pm goes to an on-call staff or has a different pay scale
This has nothing to do with whether you are exempt or not. Are you paid by the hour or by visit? I'm assuming you visit clients/patients in their homes, yes?