Well first ask her WHY she won't let you have one.
Is she afraid of snakes? Explain them to her and get a book (The Corn Snake Manual by Bill and Kathy Love is GREAT!) and help her learn about them. I remember one of my friends was like, "Eww I don't like them because they always flick their tongues out." Once I explained that's how they smell things, he was like, "Oh, is that all? That's not gross then." Actually, my mom is still scared of snakes but I promised I wouldn't bring mine near her, ever, unless I had permission.
Does she think you're not responsible enough?
Then you have to show her that you ARE responsible enough. Do your chores without being told, etc.
Does she not like that the snake will eat mice?
Well this is something she'll have to get over if she is going to let you have a snake. My mother hates mice but she allows me to keep frozen ones in the freezer as long as she can't see them. I wrap them in 6 opaque plastic bags. She says she'd rather have dead mice in the freezer than live mice anywhere near her. There is also something called T Rex Snake Steak sausages. These are like small sausages made up of ground up animals (not too different from our hot dog sausages then, hm..?
). You can keep them in the freezer and thaw them out before each feeding.
Is there not enough room in the house for a tank big enough for the snake?
You could probably find some way to ingeniously fit the tank somewhere where it won't get in the way.
Are there financial problems?
Well, if this is the reason, there's probably not much chance that you will be able to get a snake. It does cost quite a bit for a tank, heating pad/heat lamp, substrate, snake itself, mice, etc. I think I ended up paying somewhere in between $120-160 for everything when I went to get my first snake. And this was out of my own pocket.
When I wanted to get my own snake last October-November-December, I had to be a perfect child in order to get permission to get my own snake. I got straight A's in my report card, practiced at least one of piano every weekday and at least 3 every weekend, kept my room immaculate, washed the dishes, folded the laundry, etc etc etc. Well it paid off..I got my own snake in December and now in June I am getting another one in a few days.
Two is the maximum for now though.
I could ramble on some more about this and that but I do have my Math Regents tomorrow afternoon so I'd better go study. Good luck !