Continuity mistake: When Inga, Frederick, and Igor reach the secret library, Frederick reaches for the door knob to grasp it with his right hand, but the view from inside the room showing them entering has Frederick's right hand opening the door without using the knob.
Young Frankenstein (1974)
Ending / spoiler
Directed by: Mel Brooks
Starring: Peter Boyle, Gene Wilder, Teri Garr, Madeline Kahn, Marty Feldman
Fredrick gives the Monster half his brain. Fredrick and Inga get married. The Monster and Elizabeth get married.
Craig
More mistakes in Young Frankenstein
[A wolf is heard howling in the distance.]
Inga: Werewolf.
Frederick: Werewolf?
Igor: There.
Frederick: What?
Igor: [Points to moors] There wolf. [Points forward] There castle.
Frederick: Why are you talking like that?
Igor: I though you wanted to.
Frederick: No, I don't want to.
Igor: Suit yourself. I'm easy.
Trivia: When the Burgermeister says the village and townspeople were terrorized "five times before", it is a reference to incidents from five Frankenstein films: Frankenstein, Bride of Frankenstein, Son of Frankenstein, Ghost of Frankenstein, and House of Frankenstein.
More questions & answers from Young Frankenstein
Answer: She most likely missed Frederick and wanted to be with him.