Make sure you order your childs meal, don't take it for granted the travel agent will do it. I didn't one way, and DS1 (3.5) had to wait and got an adult meal. Coming back, I did, and he got a snack as soon as on the plane and child meal served before adult.
Recommend getting a night flight if you can. If she has favourite movies, download to your ipod/iphone/netbook and take that as a backup. They tend to only have 1 or 2 child movies. I've bought DS headphones rather than earbuds which I take, so he doesn't have to hold the earbuds in.
TBH, it will depend on what she likes to do. My DS, just watches films, I hope DS2 will be the same. I take stickers, crayons and paper as a backup, but he never uses it. I also took some lego minifigures in packets, for surprise toy opening, again, I didn't need them.
Take snacks she will like and get her favourite drink airside to take on.
It will be fine, remember it has an end, it's only 11hrs. I took DS1 and DS2 (4mo) to NZ in January without DH, and it was very easy. Everyone thought I was mad, but I knew if it was a nightmare, eventually we'd get there, and it would be ALRIGHT!