I would say private lessons are best to begin with. As for type of guitar and style, it all depends on the music she likes and would like to play. If you want her to stand the best chance of continuing to play, it has to be music that excites her.
As for how many hours per week, it's not really that important. The most important thing for you is to be supportive, but never force her to practice. That is the quickest way to stop her playing.
Once she learns the basics she may decide she doesn't need a teacher any more and goes to teaching herself. This is fine too and is the best route for some people.
Good luck, relax and just let her enjoy the process.