I don't know much about the Luna. If she was a little lighter I'd sell you my Moment for $100 but it will be too small for her. I think you should look on ebay and an kijiji for a used beginner board. You can find some good deals that include bindings out there.
K2 Moment Snowboard 150 cm - Edmonton Sports Goods For Sale - Kijiji Edmonton Canada.
You just have to look.
That way you can upgrade later if she really likes the sport. In a couple of years you'll also be better able to tell what kind of rider she is therefore what type of board would fit her best.