My nephew is at private school and has to do all his homework, or at least a lot of it electronically. He had a clapped out pc for ages, that broke, so he used the family pc, now someone has given him a clapped out laptop! My ds's are still little, and have only just started school. We're much less well off than my sister, so I can't imagine that we will afford two laptops for the ds's. but we also live in a pretty deprived area so I would imagine their peer's families will be in a similar boat. I suspect they will get a pc in their room or down here to share and then they will be able to use my laptop if needed. I think the upper school they will go to has a study centre too, so they will be able to use computers there, which is why the place exists, I guess, for those who don't have them at home.
I do think it's really normal for nephew and his peers to have laptops, and to be honest if families can afford it, the kids WILL have more than those who don't. That's just the way it is. There's no point being all outraged, I suspect if we could all afford it, all of us would probably buy them things that they wanted a bit more readily. Maybe not computers for some, but what about other things, like oh I dont know, pets, clothes, sports equipment or lessons, musical instruments, more expensive books or whatever.
If she's paid the money back, with interest, and you've had a stern talk, OP, then I think you've done all you needed to. Kids do do stupid things sometimes...irrespective of wether they own macbooks or not. I would gen up on the router password, etc, though, just so they dont get access to all the grot on the net 