Hi Tama-Love,
Any question about puberty and growing is welcome here!
Unfortunately, despite what they try to tell us in science, leg hairs have this nasty tendancy to grow bigger, thicker, blacker and scarier the more and the longer you shave.
What can you do to stop that? There are a few different things. One is to get laser hair removal. That is a quick fix but it costs lots of and lots of $$$. Another alternative is to try waxing. Waxing rips out the hair at the root and it takes much longer for the hair to grow back and in theory it is also supposed to grow back softer as well. Waxing can be done at home with a kit but it is nastily painful and you need to let the hair grow back quite long before you can do it again.
The other thing is the use of some depilatory creams (hair removal creams). There are some brands out there that claim to be able to make your hair grow back lighter and softer... That might be worth investigating. It is a time consuming process too. You cover your legs in the cream and sit around for 10 minutes before you get to wash it off. I might also add that the stuff is not cheap and you will only get a few uses out of the bottle.
Now as far as your Mum goes... why is it that you want to shave your legs? Remember that unlike periods... your leg hair doesn't go away at 50 years old and you will be doing the shaving bit for the REST OF YOUR LIFE! Unlike periods you will be shaving every week (some people get to the stage where they do it every day). It is not fun.. it is a pain to have to keep up with all for the sake of supposedly looking good.
You are at an age where noone will really be expecting you to shave so if I were you I'd be putting it off as long as possible!
Having said that.. if you feel that this is something that you really want to do and you want to do it right now then you have to talk to your Mum and explain why it is you want to start shaving. Don't expect her to be happy. My Mum did everything in her power to convince me otherwise and was less than pleasant when I said that I had decided to go ahead and do it.. (she'd given me razors and I had hesitated after she told me about hairy legs and did all the discouraging!). But you do need to talk to her - she's not psychic!