I had my jaw broken this past summer actually, however, i only had it wired for a week. I stayed in the hospital for a couple of days, but it really wasn't all that bad. The hosptial i was at anyways was really good, and the oxygen mask that they put on, well don't worry at allll about that. It helps you breath SO much, its really good. As for the talking bit, it is kind of hard, but she will most likely be able to talk. Its tough at first, but you adapt, and talking definitely wasn't a huge problem.
As for the pain, well they will give her good medication, and to be honest i was never in that much pain at all. I remember being so scared going into it, but as long as you are supportive it should go fine. The only real pain i remember is just headaches .. well they were pretty bad, but if you can get stuff for that i honestly don't think that it will be unbearable at any means.
As for the diet .. well she won't be able to eat much as i assume you know, but i do want to point out that she can't eat ice cream! It is sad

i remember they gave me ice cream while i was in the hospital and i was like "ugh thanks ... but i can't eat it!" Stick with protein shakes and make sure she gets enough calories. While i was on this liquid diet i lost about 5 pounds in a week (although they say that you shouldn't lose more than 3 i think?) but i wasn't up for eating. The meds they will give her will most likely reduce her apetite, so its important to make sure she gets those calories. Soup is a good way, or even just drinking lots of milk. I also ate yops - the yogurt things, and those are pretty good too.
As for the brushing teeth thing... well i guess thats a bit tricky. After a couple days i was able to use a little kids tooth brush because the bristles are softer, and just make sure that she is mouth-washing alot .. that was my way of cleaning for the first bit!
I hope that this was helpful, and if you have any more questions please feel free to ask!!
Jacq