Many thanks for all the interesting answers.
My wife fell off whilst almost stationary.
She let go of the handlebars which swung round, as they do, tipping her sideways.
I think stabilizers are not such a bad idea, but worry that on cornering they might tip you over.
We did have a smaller folder she rode. As in the comments above, the low position meant pedaling for any distance was inefficient, and ruts and pebbles tended to push her off track.
I have just repaired the battery on her Windsor (blown fuse) and been out riding it. We live in Torquay, which has very steep hills and a sea-front one can not cycle along as the Council say they could lose their Blue Flag status.
It seems a cycle track would be deemed a hazard to pedestrians. ( Insane rules ! ).
The Windsor felt perfectly stable, but not very powerful.
I did let the handle bars swing round to feel the effect and it does encourage a tumble if there is a steep camber.
I weighed the bike and it is around twenty kilos without the battery, hence pretty light as the average bike goes.
Hardly seems worth changing to gain just one or two K.
I do keep telling my better half it was her own fault she fell over, but she is hard to convince.
I feel sure the first dealer to sell a smaller framed ladies bike will do very well.
Pre-electric, my wife rode a nice light Dawes Red Feather. Should have bought the electric wheel for that one, but I really am not much of a mechanic and fear it could be beyond my capabilities to install.
Again, many thanks.