Hi, Lindsey!
Believe me, the Cast Members at Walt Disney World restaurants have seen (and served) it all! Your daughter's eating style will not raise an eyebrow, and you are welcome to bring in any kind of foods that will keep her happy and comfortable.
While table service credits are typically only to be used for meals at restaurants, it is possible that you'll be able to "swap" a table service credit (more expensive) for a snack (less expensive). Each case is individual, and will be at the discretion of the Cast Member you are asking. I've heard loads of success stories with that switch; going from snack to table service certainly will require a paid upgrade.
Any unused credits on your
Disney Dining Plan will expire at midnight on the last day of your Resort stay.
Have a wonderful trip!
See you later, celebrator,
-Deborah B.