my son broke his hip three years ago when he was 8. because of the point of the break he was put into a body cast exactly like your daughter will have. i can't help you out with diapering, but as far as car safety, buckle her in as best as you can. and to keep her busy we went through lots of coloring books, legos(duplos), play-dough, childen's videos and hot wheels. we bought an inexpensive air mattress and let him lay on the floor to play. it won't be easy, we saw a pamphlet on casting of this sort and the ingenius ways people help children get around. good luck!