I agree with Knott, tell her you're not keen on doing the leg extensions and that you'd be interested in learning some closed chain kinetic exercises that work the same muscles and are more functionally applicable for you.

Re to back to back days, I also agree. Unless they have a very good reason, ie treatment on the second day will be different that the other and is needed to get some sort of necessary treatment in... I'd cancel one of them and if it was me, I'd cancel Wed. I never have patient's on back to back days unless there is something that has to be done by the PT that can't be done on their own and is necessary for a good outcome. This is sometimes the case with very new injuries or post surgical patients. It doesn't seem to me like you fall into that category.

I hate to say this but... some PT clinics are all about the money and will push for the other appointment for that reason. They will also sometimes feel like they can make you dependent on treatment at the clinic by using machines that you don't have access to at home. If they only give you exercises you can do at home, how are they going to keep you coming in? This kind of behaviour ticks me off.