She’s 4 years old I don’t think it’s wise to do it young like this because what if when they’re older they don’t want it, piercings are a form of body modification and should be decided by the person who’s receiving said mods. Sorry if I sound bitchy but I come from a piercing and tattooing background and I believe in self expression and getting any type of piercing or tattoo is a very “intimate” thing to oneself so you may wanna wait and let her make that decision