Convincing your parents to let you lease a horse?

I have been riding for 7 years and would love to lease a horse! My mom said she would love for me to have one (money's not a problem, my mom used to take care of her neighbors horse everyday and she understands how expensive and time consuming a horse is), but I need to be more responsible. I understand that leasing a horse before buying is a good option, because it will prepare me for what real horse ownership will be like. I go to my neighbors barn every day and do free barn chores, do my chores, and take care of the pets I already have. I was wondering if anyone had any ideas about any extra things that I could do to prove I was responsible enough to care for a horse? I want a horse more than anything else in the world, and I just need to prove to my mom that I am responsible enough to take care of a horse. Please no rude or mean answers, thank you so much!