Re: How to tell

If the facial hair doesn't seem to bother her, than I wouldn't say anything. She is most likely aware of it, and you telling her what she already knows is likey to affect her self esteem. And it is quite possible that you will get into a "you should love me for who I am!..." type argument. You may say that this is not the case, but she may still feel it is.
Females often have pretty low self esteems WITHOUT you telling them of a physical fault. Also, a lot of us are used to gossipers, we have people talking about us all through school and we have experience in how to handle it. Trust your girlfriend to be able to handle it. Also once she started waxing the hair or whatever, she will need to do it more and more frequently which could be a hassle, not to mention expensive, and then she may end up having to do it almost everyday, like guys with shaving.
But then, its up to you what you decide to tell or not tell her!