A restricted mid drive pedelec ebike in the UK is going to have a 25km/h (15.5 mph) limit on the assist. While she could go faster than that through her own input, it's not exactly easy for someone who is a little unfit or not really much of a cyclist.
On the other hand, something like a Shimano esteps 6100 or a Bosch active line is going to help her get to that speed very quickly in all but the worst conditions, and maintain that 25km/h speed without any difficulty. You'll find that her average speed on an open road will be pretty close to that number, the motor really helps to flatten the hills and knock out the effects of a headwind.
Something like a Gazelle orange or a Merida Espresso would be just about right.