I wanted to get a belly button piercing when I was 15 and my parents said absolutely not, if I did I would not be allowed to get my drivers license. So I got one. Loved it and Still to this day do not regret it. I will never have a body like that again, and it wasn't something I did for boys, I thought it looked cool. I have had 2 kids and the piercing area does not look distorted or awful. I agree with PP that she should wait to see if she still wants it.
In terms Of what other people think, honestly who cares? We constantly tell our children that they should not care what other people think, same goes for this.
I am however very anti tattoo. Since they are forever and definitely fade, look bad over time.