I've not leased a horse out before, but I have bought/trained/sold a good few. You might want to consider legal ramifications in addition to any ethical ones about the care the horse receives. If she kicks someone and they have to go to the ER, whose fault is it? Is is yours, since you technically own the horse? Is it the leasee's fault, since they're currently the ones caring for the horse? Will you have any rules about safety equipment to be used whilst riding/handling her (e.g., helmet, hard toe boots)? Are you going to have a formal contract set up, signed by both you and the leasee (and a parent/guardian if the leasee is a minor) or will it be an informal handshake agreement?
A few others might be- are you going to want to supervise how she's handled/trained (e.g., what bit is used on her, what events she's trained in)? Will this be a "you lease the horse, she belongs to you and you (leasee) cover all expenses/care/etc until the lease expires" or will you be more hands-on? Who will pay for the vet bill if the horse somehow injures herself in a freak accident? Will you split it, since you own the horse, or will the leasee preferably cover all of it since they're responsible for the horse?
These are some of the things I'd want to consider before getting ready to find a leasee. If you prep for problems now you can save a headache in the long run. Best of luck to you! <3
(edited for clarity, brain goes brr faster than I type)
Edited at June 16, 2021 10:45 PM by The Lady of Fangorn