Sudden loss of power shouldn't result in a fall, but a throttle contolled e-assist would completely remove that risk.
Yes, I felt that that would be the case, & in fact one of my reasons for suggesting a 2 wheeler is that I think she might find she can ride one fine - her son has recently bought her a 2 wheeled folder (make as yet frustratingly unidentified so it could be awful!) She wants to cycle short distances on the flat to improve her fitness, so a throttle assist may not be the answer in her particular case, although I can see it could be very good for someone who wanted to cycle further.
Stabilisers fundamentally change the way a bike handles, so caution is required.
Yes, and I think a trike would need a different riding style too. I must say I wouldn't fancy using stabilisers much myself, but was hoping they might be a useful intermediate step, and cheaper and less difficult to store and lift than a trike given her particular circumstances. But perhaps I'm being over optimistic? I might wait until the folder arrives & suggest she splash out some money on stabilisers to try them - it would be less of an outlay than a three wheeler, and where we live in mid Wales there isn't much chance to give one a test ride.