It sounds like she wants something simple, and you want something inexpensive:
If she wants strength in her legs, and maybe her abdominals, then squats and situps/crunches/planks are great. Only need a couple exercises, and no equipment.
If she wants to get her heart going, and has no time to walk/run/bike/hike etc., she could skip rope (like you), or she could get into hopping around exercises (jumping jacks, mountain climbers, burpees).
Barring all that, a used elliptical is a great idea, provided you have the space. If she goes really fast for a bit (15-30 seconds even), then slow for awhile, rinse and repeat, then she can get a crazy good cardio workout in 10 minutes. If you buy used, shouldn't cost much either (we got ours for $200).
Personally, (note, I'm a slim 26 year old male with no watermelons in me) I just do pushups, pullups, squats, crunches, and planks. On a good day I then do burpees until I start to feel like I'm dying. :) I figure that until I'm awesome at these basics, I won't bother doing anything more complicated, though bodyweight ninjas are pretty awesome.