I find it hard to believe there is a girl out there that doesn't wear makeup but wants to. Usually if a girl wants to wear makeup ...she will be wearing makeup. Half the fun about make up is just fooling around with it and trying different things. However, back to your point. You could buy her a spa day. When you go to the spa to purchase the certificate for her, they will ask you what you what like included on it. You could have them include: massage, facial, and professional make up application.
That way, it looks like its just part of the "package" and your not just singling out a make up lesson for her.