, doesn't sound like a lot, but it's been shown that more reps with lighter weights tone muscles and burn more calories, rather than bulking up. Resistance bands
might be good option too, so she can hook her wrist or arm through it rather than using
Swimming or water exercise is also an option. The water supports the joints, lessening the impact on the knees, hips, etc.
Chair yoga, balance ball...try a variety of things and choose what works best for her.