First of all, you don't need another horse. You don't even NEED one. What is wrong with the horse you have...besides the fact that it isn't an Olympic horse? A huge majority of us don't own Olympic capable horses, so that is not a reasonable argument. Nor is the fact that some girls have more horses a reasonable argument.
So far all your reasoning sounds like you are a spoiled little girl, stamping your feet and trying to get something you want. So tell me, what is that makes you need another horse or even deserve one?
Speaking as a parent...If my daughter approached me as you have, wanting another horse based on your reasoning...then I would give it to her alright. Not the horse....but a good month of cleaning every single stall at our barn, scrubbing every water bucket, and any other menial task that comes up and she would have zero riding privileges with the horse she owns. By the end of it, I bet she would appreciate the horse she does own and understand that horse ownership is a privilege...not a need.
I can't help but feel that you are a spoiled little girl that can't even realize what an absolute privilege horse ownership is. If I am wrong, then I will happily apologize. So please tell me, why is it that you absolutely need another horse?