Hints
Taking the title and cover picture in consideration we're probably dealing with Disney princesses here...
Did you notice any scanning the grid (or clues perhaps)?
Were there any entries where you thought: "This one's getting there..."?
1 Across is a good place to start sometimes...
DIANA is one letter off TIANA, a Disney princess. Can you find the others?
The letters that need to be changed form the first part of the answer
You probably know what her full name is but if you don't...
then 6A might provide a good clue
The letters that need to be changed spell DAISY.
A hint for DUCK could have been found at 6A. Also: the first letters of those five clues involved spell DUCKY.....
Another clue was to be found at 37A, Daisy being Donald's sister-in-law.