I'm as certain as I could be without having met your daughter that it will be the fashion/peer thing that is motivating her. I suppose there could be an element of the rebellion/shock-the-parents thing, but, well, that kinda is fashionable when you're sixteen. Personally, I don't see a problem with a girl of that age having a belly button piercing - she's the one that's going to have to pay for it (unless you're a softy), keep it clean, deal with it if it did get infected, etc. - but she's your and Silver's daughter so it's your and Silver's decision whether to let her do it or make her wait another year.