Poor kid. My daughter had that, and the spreader. (at the same time) It wasn't fun, but she got used to it within a week. It is hard to eat. It's hard to talk right, and it's hard to play a wind instrument. But, she shouldn't have to wear it for the entire time she has braces. I can't remember how long my daughter had it... but, it was less than a year. (Her teeth and jaw were really bad)
It did an AMAZING job though. It was noticable very quickly, and I was so happy with the results.
For the first week, smoothies are your best friend. She will learn to tear off her food, like bread and eat it with her fingers. (not as weird as it sounds) But, taking big bites out of a hamburger or anything is probably not in her near future.
Still, it's really worth all the hassle.