When Ella and Slannen go out for dinner, he starts to tell her that he wanted to become a lawyer, but he stops and says, "Forget it, it's silly," she presses him some more about it until he tells her. But later, when they're about to be eaten by the ogres, and they tell her to get in the pot, she starts to do it, but Slannen tells her to forget them. She forgets them and asks who they are. She obeys then, but doesn't when Slannen told her to forget it when they were having dinner.
When Slannen the elf frees Ella from prison, Ella opens Benny to find out where Edgar is. When she opens the book she opens to the first page. In the next shot the book's pages have been opened to the middle.
"When Char takes Ella to the hall of mirrors, he holds both of her hands. Later, when the clock reaches 12, Ella has the dagger though there were no places in which she could have kept the dagger without Char seeing." Considering Ella had Slannen chain her to a tree in an attempt to keep her from killing Char, it's safe to assume she did away with the dagger, thus she didn't have it with her when Char took her to the Hall of Mirrors. However, Sir Edgar specifically ordered her to kill Char with that particular dagger. She couldn't go and find the dagger because she had also been ordered to kill him at the stroke of midnight, so the curse made it magically appear in her hand to allow her to obey her orders.
Ella's enchantment fails on at least two occasions: when Prince Charmont says "Allow me" and she continues to refuse his help, and when Slannen says "Forget it" and she continues to discuss his legal aspirations. The earlier "bite me" scene established that Ella's enchantment takes colloquial "commands" literally, thus she should have allowed Char to help her, and literally forgotten about Slannen's peeves.