I would suggest keep this client moving as much as possible (treadmill, bike or walking). Some exercises with band might be an option and then some light free weights (machines could also be a great alternative). Make sure this client checks his blood sugar before exercising and as long as he/she has available some type of food or a drink with some sugar in it close by, then it should ok. The exercises and the duration of the cardio/workout should be at a level that your client can maintain for the entire duration of his/her workout, if not then adjustments need to be made. Medical clearance is a must (as Sue suggested).