Your orthodontist will have a list of things she needs to avoid. Stick to them, or you'll have broken wires and a mess of other problems. She MAY be allowed sugar free gum. Seems to vary by orthodontist. She also needs to learn how to brush and floss around the braces to avoid bad breath and cavity problems later. We also invested in several extra packs of wax (can be found at the drug store) and I think it was Orajel that makes a numbing spray that one of the kids really liked.
We also had to keep on them for wearing the retainer properly later. I think that was the harder part for us. The excuses abounded. They both hated the retainer.
Any time she gets them tightened, let her eat softer foods and give her Tylenol. It can really make her mouth ache.
Also, don't be afraid to find another orthodontist if you don't like the person you're dealing with. You'll be dealing with braces (retainers) for years. Like/trust who you have. We had an issue with one doctor, so we switched, even though it was out of network. If you can find an orthodontist that has a flat fee, it will help keep costs down later. I much preferred that the second time around. The first time (and first orthodontist) charged for every little thing and it seemed we were always in there. Just dealing with him was unpleasant on top of that. We're so glad we switched. Just keep it in mind.
When the braces came off, we had a party with all the stuff they couldn't eat for the duration.
Good luck!
P.S. If your daughter likes popcorn, try Pirate Booty. It's a puffed snack that's a lot like popcorn, but no kernels to get caught in braces.