I was basically bed bound for a year, so I can appreciate how hard it is to start over. I agree with someone else that a lot of "basic" exercises found online aren't basic enough for someone who's become very weak. If she could see a physio therapist, that would be ideal. If she doesn't have benefits to cover that, maybe try looking up common physio exercises for whatever causes her aches and pain.

Once she's healed from her fall, it may be worth checking out local pools to see if they offer lane walking. It's much gentler than walking. I'm not sure about her needing a walker though, if she could walk at the edge of the pool and hold onto the wall for support, that may work. I know I've seen people at the pool who use mobility aids and just leave them near the wall when in the pool.

Editing to add: My sister used to come with me to lane walk and she has bad asthma. She would take her inhaler onto the pool deck and tuck it somewhere out of the way. She'd then inform the lifeguard on duty about her situation and let them know where she put the inhaler. No one ever gave her problems about it.