Back surgery is definitely nothing to mess with, although it must have been serious if after several YEARS she still isn't supposed to lift anything heavy. At any rate, priority #1 is getting the exercise cleared with her doctor. Another important issue is to figure out what her goals are. Does she want to exercise just to help with weight loss? Or is she actually interested in increasing her fitness?
Depending on what she's allowed to do and assuming fitness is the goal (not just burning calories), I'd probably go with a gentle progression like so:
1. Light cardio to build a base of fitness. Walking, running, rowing, biking, swimming, jump rope, and elliptical can all be done at an easy pace and are a nice way to ease back into exercise. Increase mileage/speed/intensity gradually. Most of these should be just fine even after back surgery.
2. After the cardio, or alongside it, start with some basic bodyweight exercises. Again, these should be doable even after back surgery. Depending on her abilities, pick exercises for a full body routine that includes the lower body and upper body equally. Good exercises to pick from include air squats, jump squats, one legged squats, lunges, step-ups, push-ups, clapping push-ups, handstand push-ups, pull-ups, muscle-ups, sit-ups, superman, levers and so on. For example,
here is a routine very similar to Starting Strength, except using only bodyweight.
3. If everything is going ok and the doctor clears it, very slowly start add some weight training. SS or SL 5x5 are good choices, but be sure to start with the empty bar or even a lighter (15-25lb) training bar. Be extra picky on form.
4. After a base has been built, replace the cardio in #1 with something more intense. Any of the exercises listed in #1 can be done at a high intensity, such as doing time trials (complete some distance as fast as possible) or high intensity interval training (HIIT). Alternatively, you could introduce her to
Crossfit and use their workouts for both strength and conditioning. Just make sure she reads
What is Crossfit and the
Crossfit FAQ so she knows what Crossfit is all about, how to scale workouts, and so on. If heavy weights are not acceptable, here is a list of
bodyweight Crossfit workouts.
