Seconding that you still need a bill of sale, JUST IN CASE. :P
If I was going to lease my horse out, I'd expect to provide my leasee with my horse's tack. I'm too picky about how my tack fits my horse, I wouldn't want to think about the possibility that my leasee is riding my horse in a bit/saddle that I haven't approved/that doesnt fit as well as mine. On the other side of it, if I was the one doing the leasing, I wouldn't even consider leasing a horse where I'm required to provide my own tack. Part of the benefit of having a partial lease on a horse is that you don't have to invest money in things like tack.
Do you actually like having her lease Moro? Sure, the financial benefits are awesome, but it sounds like you're not really enthusiastic about sharing him (which is 100% fair, especially since you just got him gifted to you). I'd say just think about whether or not the financial benefits outweigh the freedom/lack of stress of having your horse belong to you and only you.
I knowwww not having a bill of sale in the US/UK/Europe wherever is a BIG no-go, but I swear I asked like 20 separate people here and everyone looked at me like wtf even is that before laughing and saying that thats absolutely unnecessary, and not something that's done here :p
I do want her to keep leasing Moro, not just because of the financial benefits, but because I know she cares about him too, and i would hate to just pull him out from under her when she's attached to him. Plus I probably wouldnt be able to go out to the barn every day (i would if necessary, but I'd have to skip school and drop other activities).
As for tack, everyone keeps saying that the horses' tack is the one that fits him and the one that should be used, just to clarify, SHE HAS BEEN USING HER TACK ON HIM FOR AGES, I JUST BOUGHT MINE YESTERDAY
(I borrowed a saddle from a 3rd party before!). The only thing that would change is the bridle, instead of one that came with him (which belongs to his previous owner, who needs it for their new horse), we would be using mine and hers, one with a snaffle and one with a leverage bit.
The only issue i had was that I'd rather have my own set (bridle + snaffle + leverage bit) and have her have her own set (bridle + snaffle + leverage bit) just to avoid situations like 'one of us puts it in a place where the other cant find/access it', and situations where something might break and the person who broke it wont take responsibility.
I'll talk it through with her, explain this reasoning, and it will be ok I'm sure! Thanks everyone for the advice!