As long as the clot has been verified to have dissolved, by the doctor, there shouldnt be any reason to not start cardio back up immediately. The primary risk is the clot moving. Thats why ALL exercises in the extremity that it is in should be withheld. But once its dissolved and there are no other issues you should be good to go.
Hands down, tell her to see her physician and explain her goals and what type of exercise she is interested in (cardio), tell her to have her physician advise her on the proper course of action, and get that physician to sign a release and offer some guidelines for her program and progression. If her physician can’t offer that, I’m sure the physician can refer her to someone who can. There is no substitute for covering all the bases and having proper DOCUMENTATION.
It might even be a great idea to include a short letter (no longer than a page) to her physician explaining your viewpoint and professional concerns and what you are requesting that the physician provide to the patient (your client) so that that client may share that information with you. By including a short letter that can be read in the appointment, you are expressing your professionalism and your concern for your client. This might also show your client (the patient) the true colors of the physician. If the physician is not interested in your letter and just dismisses it, your client might consider, on her own, finding another physician who cares about her life and realizes that fitness professionals are a critical link between the public and the allied health community. You are also marketing yourself to that physician, which may lead to referrals! Doctors notice those types of things! If the physician lives up to your expectations with your client, you can refer other clients to that physician, and before you know it a working professional relationship is established! Always look at any professional contact as an opportunity to market yourself in the most discreet way possible. It’s easy enough to market yourself simply by showing that you care. That’s over half the battle!
Danielle’s recommendation is right on. A blood clot is potentially life-threatening, and the condition that lead to it may still be there. She also may be on medication, and some of those medication can have side effects.
Definitely get a physician’s release. This may even give you an opportunity for establish a relationship with a doctor. Doctors often look for trainers to refer to as long as they are confident that the trainer defers to the physician. if in doubt.