Why can’t GLaDOS help solve her own tests?

In chapter 8 of Portal 2, when Wheatley apparently uses GLaDOS’ old tests, GLaDOS says: “I'd love to help you solve the tests. But I can't.” Any (logical) reason as to why this is the case? I get gameplay wise that this would be boring, having her give all the answers, but don’t understand how the writers have justified this. Can’t seem to find old discussions on this either.

edit: solved by generous commentators and my eventual progress in the game