I didn't like snakes either...wasn't scared of them anymore, but did NOT want anything to do with them. My daughter asked for one for her 13th birthday. It was the only thing she asked for in the 8 months prior to that 13th birthday. I got her book finally, told to read it cover to cover and make a list of the things that she would need. She also went to my sister's house, where I had a niece who was into reptiles (Still is and works for the big wholesaler out in California - Quality Reptiles(?)). I made sure that she knew that she was going to be able to care for it and esp. feed it.
She came back with all my requirements met. So for her 13th birthday off to the store we went... I've learned from that mistake

Bought her a lovely, beautiful little ghost female, I ended up naming Lady G (Ghost) since she couldn't seem to come up with a name that she liked. Unfortunately or fortunately, she ended up being a non-feeder and in a panic over the thought that I would be a terrible mother because *I* let her *only* birthday present die, that I was on the phone with that pet store, other pet store and then tracing down a reptile vet...
The vet did the trick and she lived until she was almost 6. She had issues that I believe trace back to those early days, but I couldn't prove it. As it was, she talked me into buying my own snake when we stopped at Tinley Park because I had called her snake my snake one too many times. I know have six with 3 or 4 more on the agenda and she's down to none
Don't be obnxious, but show your mom that you are serious about this and its not another phase you are going through... esp. if you are prone to phases

Might start buying the equipment you need to show her that you are serious about taking care of it. It's all stuff that could be stored away if she doesn't back down until the day you have your own place and can buy one anyway
Good luck