You have a lot of great answers, but I would contribute a few things after doing 10 days with four kids!
I'd say to bring princess dress up costumes with you... they are close to $70 in the park and your daughter will see a lot of them walking around and may wish she had hers. I brought dollar store glow necklaces- they were neat for the kids at night and not nearly as expensive as the ones sold at the park. Also, when the kids were dancing around to the music, we could differentiate them right away from the other kids! We also brought some snacks (granola bars, trail mix, fruit leather, beef jerky, frozen Capri Suns, and bottles of water.) I understand you might need to supplement even with the food plan. They let us take in outside food unlike many other parks. Renting a strolller is VERY expensive, so I'd recommend bringing one, preferably with some sort of tall flag or something on it since there will be 5 million JUST like yours (whatever style you have!) USE the Fast Pass options as often as possible. If you want to meet the characters outside of mealtime, there are less lines just as the park opens.
We were camping for two weeks and had 10 day passes... could only stand the parks for 9 days! LOL! I think a 7-day pass is plenty! If you camp and don't do the food plan, having a Slow Cooker was AWESOME!!! Left the parks for an already cooked dinner and a nice break and went back later for fireworks!
Good luck!