Now there are two ways of thinking. Some people say that you schould watch them in order. It makes more sence for the person watching it, easyer to follow, and its the way george ment it to be seen.
The second way is to watch it in the true to form way. Which is awsome if you core into the trilogy, but if your not, it will just cause confusion.
Since she is a girl i would assume she is not core,and has never seen the damn thing and will probably lose interest right away if you show her " A New Hope" first. Most people forget that the orignial films are a little dated. So most people will not see the point in even watching it, getting bored, and just quit on it.
The newer films are more modern, with better effects/ more action. To get people interested this is the way to go.
May the Force be with you young padawan.