I waited until I was 19 to get my eyebrow pierced. I did it on spring break while I was in college. It was a very thin, small, gold ring. I thought it was pretty...for about a month. Then I took it out. I let it heal over. Luckily, I don't have a visible scar - I do have a very tiny scar, but it's hidden behind my eyebrow. My best friend went off and got her tongue pierced at 16 against her parent's wishes, and practically incurred the wrath of God from her stepdad. He made her take it out, of course. So it was totally not worth it in the end. She ended up getting it redone when she turned 18.

Anyway, I hate to say it, but I see your mom's points. Basically all you can do is ask nicely at what age you will be allowed to get it done. Then count down the days until you can do it with her permission. There's no point in doing it without, since you can't really hide a nose ring, and fighting with her about it will only drive her crazy and get her ticked off at you. She's probably just trying to make you wait for a year or two to make sure it's what you really want to do. Hang in there!