If you are working in the UK, The Wikipedia reference-linkparkinson's disease society has a brilliant exercise booklet which your patient can get for free.
Do you know when this patient is last seen by a neuro consultant for review of her drugs? In general they should be seen one time a year but in reality this is not true in all cases I am afraid. She is also having some divertion to the left after some time which could mean that her medication is 'running out'.
You have to ask yourself what you want to achieve because a short period of exercises will not help your patient. With what you write I would say that she is already in a 'progressed' stage and adjusting her enviroment might be important.