Hi KRC welcome to the forum. Wow what great advice from everybody. I'm sure you feel you've asked the right people for help. Are you starting to get an idea of what might be the right choice?
I would echo the recommendations to make a trip with your Mum to test ride a few because when she finds a bike she is comfortable on and the way the power responds to her feels right she will use it and it may just be the best gift since her iPad (assuming she has one - several older customers have told me this
...
Have you checked out the forum dealer locator:
http://www.pedelecs.co.uk/buy/electric-bike-dealer-directory/
there are few in the region although I don't know how close to your mum.
One suggestion I can add to all the good advice above is to consider the next 5 or so years and whether a step through or at least low cross bar would be sensible.
No one replied regarding the D-cycle - they are probably one of the better quality options sub £1000 for the money but a bit heavy and not the best on hills.
Probably the best torque sensing ebike sub £1000 would be the newly priced Wisper models. check out AMPs link at the top of the page. These offer significant help on hills.
Hope that adds to help already offered.
Any questions regarding models just ask.