I haven't had the opportunity to look yet, but I'm hoping to find some pre-written leasing legalese that I can borrow from. She's 17, so her mom will be doing the signing. I haven't seen her ride yet. I have seen many photos, and she has a fantastic position. She also managed to school her horse in some training level dressage. I would retain responsibility for normal upkeep, i.e., farrier, worming, teeth, boosters. I would also insist on riding him myself 2 to 3 times a week. It would be a partial lease only. I wouldn't mind her taking him to shows, on the condition that someone I know, preferably me, goes along. There will have to be many forms for the signing. It's true that waivers aren't legally binding, but they are compelling to a judge or arbiter. It's definitely worth having them signed.
The other expense defraying option is to let my instructor use him as a lesson horse. I like this idea less and I'm not sure she'd like it either since the horse is 16hh. I don't want some scared beginner tearing up his mouth.