cycling on a lot of resistance will make your bum bigger, squats aren't too bad for your ankles at all. but it also works on the top of your legs and not really the bottom that much. i'd recommend skipping, you can potentially hurt yourself.
1. Squats can strain the Achilles tendon, last I checked this was in the ankle. Also squats require ankle flexion this could aggravate an injury.
2. Proper squats do work the
front of the legs (quads) but also equally work the
back of your legs, hamstrings and glutes in particular.
3. Skipping is a ridiculously bad idea depending on the type of damage she has in her ankles.
4. The wobble-board which you mention is probably good and you are right that damaged ankles need specific attention.
Stretching can improve leg tone, as it strengthens muscle fibers as well as elongating connective tissue.
This is absurd. Tone is the result of reduced bodyfat % and the size of the underlying muscle (primarily the former). Stretching does neither of these things and absolutely will not result in increased tone. Stretching also does not strengthen muscle fibres or connective tissue, it actually weakens muscles for several hours.
Which is not to say that stretching is not a good thing. A high-level explanation of stretching is that it improves flexibility. Improved flexibility may improve exercise form and may reduce injury.
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As for advice for AyO:
1. See a Physio about rehab exercises for the ankle.
2. Consider surgical treatment if relevant
3. Fix whatever the ankle problem is
4. Do weights (powerlifting and olympic lifting)
5. Do pushups, pullups and dips
6. Run. Row. Swim. Ride.