That's just ridiculous.
A- she is the one keeping time (actually that would bother me a lot- I need to see how much time I've got left- my T has one clock next to him- for clients to see and a another one on the wall behind the client- so T can check time while looking at the client)
B- 10 mins for 75 USD? Like really? How much do you pay for 45-50 mins?

I don't think this is legal- either you two have to decide beforehand to have a 60 min sessions or she must get you out in 45/50 mins or let you know this is happening.