(A note to all Panel readers out there: You can submit as many questions to the Panel as you like and it's much easier for us if you submit questions individually rather than ask several in one post. You will get better and more detailed answers if you ask Qs one at a time)
Here are the answers to your questions:
1. Yes, you can bring food and water into the parks. You can't bring large hard-sided coolers or coolers on wheels, but if you can easily carry the food in a backpack, then you're fine.
2. Check out
this post, which is a discussion I had with my 11 year old daughter about her favorite things at WDW. Perhaps this will give you some birthday ideas. Also check
here for other birthday tips.
3. I'm so sorry for your loss. Perhaps you could plan some activity in remembrance of the lost family member. If she liked music, then see a concert at the House of Blues, or if she loved Italian food, plan a meal at Tutto Italia and toast to her memory. Disney Mom Laura had some nice thoughts for a family in a similar situation
here.
I hope you all have a magical and memorable trip.