Ah excellent! Yes you need to be gentle with her!
In your part of the world people seem to walk along the sidewalk above the long Tableview/Blaauwberg Beach stretch, which is flat and has restaurants to stop for a drink.
A bit further away is the Sea Point Promenade...
More my side are these Constantia green-belts. There is also the flat Tokai Forest loop of about 4km with a Secret Cafe selling coffee and pastries most days, about half way around.
Then there's the Muizenberg to Kalk Bay walk past St James - but that is a proper drive to set up!
Indeed @JasperDick and @ZakLudick. Flat and stable should be fine. I'm not sure how far I can go, but it's standing still that hurts. Shop queues and if I overdo it in the kitchen. Lord knows I miss being in nature and smelling the fresh air. Apparently cycling would be good for me. It will increase mobility without putting strain on my knee ligaments. Swimming too, obviously, is excellent.