Send an anonymous email to someone

I have a girlfriend who doesnt know that she has this really bad habit of burping right after a meal; in public. To her, it's normal. But for me , it certainly isnt ladylike at all. I've always wanted to let her know how disgusting it is but cant bring myself to tell her. A friend suggested that i send her an Anonymous Email which is 100% untraceable. I hope this will finally drill it into her that this habit is really disgusting.