Depending on how far she would want to ride, and how much battery assist is used, the 400w battery could be an issue.
I have a 400w battery and a 500w battery, using the more common Bosch system.
The Bosch motor is slightly more common than the Yamaha unit, but I’m sure the Yamaha unit is fine.
I get about 30 miles quite easily using the 400w battery, but use the lowest assist level for about 90% of the riding time.
Using more assist than this will eat into the range.
The current colder temperatures will also affect the range.
My advice would be to have a bike with a 500w battery.
Be aware though, that batteries are expensive, the Bosch battery (500w), is £700!
Can’t comment on the actual ebike, but I do have an e fat bike hardtail, wouldn’t want a normal hardtail as the e fat bike is slightly more comfortable, plus you don’t need to worry about the increased drag.
Haibike sell a e fat bike hardtail, or there is an offer on at present for my bike.
Have a search online for the Felt Lebowske, feel free to email me if needed.
I’m not connected in any way with the deal etc.