I guess time will tell. I imagine the status of the lane will be relevant? I don't think riding ebikes "off road" is illegal regardless of the riders age, but the same is certainly not true of official footpaths & bridleways. Surely the parents will take this further, if the kid was on drugs which should be simple enough to prove.
In your world and mine, probably, but even then it might depend on how well the two families are acquainted. Without being a snob about it, taking it further in the sort of community where it's normal for 14yr old girls to be ferried around by Drug taking 15yr old boys might not be considered or advisable.
This is a shame. I don't agree with a lot of her politics, but have long admired her spirit, determination, desire and ability to get things done. She's also down to earth and has a personality, shown on programmes like 'Have I got News for you'. https://www.bbc.co.uk/news/articles/cglpz89265jo
e Ebikes aren't illegal if the motor cuts out at 15.5 mph is my understanding. Once you 'jailbreak' the motor and it can travel above that imposed limit it becomes a motorcycle with all the relevant restrictions that apply. Unless of course it's ridden on private land.