"She says you have to change one letter, so the answer's probably some sort of word game. Her choice of words is suspicious to say the least. Try and think of some kind of dessert that you can make by changing a letter in... Ah, I've got it!"
"Huh?! What is it? What is it?!"
"Forget changing a whole letter... You only need to change one line. In fact, that pretty much gives you the answer."