My friend told me how to ride my horse? What to do?

So today I let a friend of mine hop on my TB gelding to just do flat work [we ride hunter/jumper] and I rode a school horse. She then preceeded to tell me how to ride my horse. My horse is just a little neuroic and can get high strung at time. A lot of his quirks are just nervousness and I don't punish him for it. Anyways the point is, I kind of got angry because this is the first time she rode my horse. She tells me how to do a lot of things at the barn and is pretty critical and rude a lot. I normally just inorge it and just try to move on with my task however this really got to me. She also asked to ride my horse tomorrow and on thursday. I really didn't even want her today but surcame to peer presure. How do I tell her no? Is it okay to be a little fustrated with this girl?