Should a 13 year old get a navel(belly on) piercing?

A situation like this is entirely in your hands, since the piercer will not pierce her without your consent. No one will look at her funny, since most people probably won't know if she's not showing off. The piercing won't make her look any older, which I don't think is an issue anyway, seeing how mature she is in the first place. I think if there's any girl out there who deserves it, it's your daughter. Obviously you did something right if she's that responsible, and I think you should be proud to reward her with that level of trust. It sounds like your mind is already made up, and you just want reurance to make sure you're still being responsible. Well, if it means anything to you, I think you're doing the right thing! Go for it!