you can certainly ask her to remove her piercing for the day and cover up her tattoo if you wish. BUT (i'm sooooo going to get flamed now :shame: ) i don't think you have a right to get upset with her for having tattoos and piercings when she did. your life probably revolves very much around the wedding right now, but i very much doubt hers does, or that she even thought about that when she had them done. if someone went bridezilla on me for having that done (not that i would... i don't think anyway!) i'd probably have some serious second thoughts about even being a bridesmaid.
I never even came close to goin Bridezilla on anyone!! And honestly, like someone else said, I do not want that in my expensive wedding photos!!! It is a once in a lifetime thing, and I do not want the photos to look trashy, and with that stuff showing, it surely will.