of course, you need medical clearance for this client and do an assessment as you would do for any other person.
With a history like this, it is rather certain that she has been in physical therapy for some time and should have PT instructions for exercises. With a bit of luck, you may even be able to talk to the physical therapist even though the surgery was a few years ago. You may also get some information from the doctor about restrictions, if there are any.
I usually start with the PT exercises and the results of my own assessment and slowly take it from there. Sometimes, vigorous cardiovascular exercise is not a good option, no matter how desirable to support weight loss. Losing weight, though, would certainly help, and 30 lbs. fortunately is not such a big number to make this a goal which can only be reached in years.
I wish you good luck.