TRX might be a little too advanced for a person of that age, especially if she is getting dizzy and you’re not sure why.
I love getting a patient’s history, FIRST. What is her typical day like? When was the last time she was in an exercise program? When was last time she seen a doctor? Resting HR? Resting BP? What is her medical/orthopedic history? etc etc. This helps me better manage the program and I can have an idea of what to expect or possible complications when training them.
Also, she may be suffering from a condition simply called hypoglycemia. Is she eating before her workouts? If so, what, how much and how soon prior to exercising does she eat? Could be dehydration or a number of things. But that is where the medical history helps.
I also agree that it may warrant a visit to her doctor, unless the visit was recent. It may simply be that the workout is too intense for her and scaling back the intensity for what is right for her.
I agree that she needs to see her doctor. I have had younger clients that would get dizzy or lightheaded from circuit training with 2-3 strength training exercises in a row, but in a younger person it is less alarming. The fact that it lasts a few hours is particularly noteworthy. Have her contact her doctor.
Dizziness can be caused by a number of different reasons. I would HIGHLY recommend that you insist that your client see her physician before doing any further training. While it could be something fairly benign, it could also be something more serious. It’s ALWAYS better safe than sorry. If this were me with one of my clients, I would INSIST that she see her physician about this issue BEFORE she works out again (either with me as her trainer or alone).
My two cents.