I’m with the others – get in touch with your client’s physician’s office & see what’s up. They’ll give you some recommendations based on the history. It’s always better to be safe than sorry.
And ask for contraindicated exercises/activities. I would stay away from plyo exercises and make sure you client doesn’t have other issues like high blood pressure, peripheral vascular disease, etc. For some people with varicose veins certain activities can result in discomfort. Encourage feedback from the client to make sure you avoid or alter such activities. There are a few things that I could include, but I am not a physician. I would do some research and ask their physician for clearance to act on what you find.