How is it obvious when she was repeatedly talking about the return of Black Empire. It's only after she's released in Ny'alotha that she reveals her true (?) motive. And for all we know, she might have said that only for us to spare her.
Even if that was her plan... What made her believe it's possible? She didn't have the dagger before 8.2. So did she flip on N'zoth after 10k years? What exactly did she plan to do to him? She wasn't anything special during her encounter, and it took a lot of what Azshara doesn't have (HoA) to be able to defeat him. Was she going to cast a spell and that's it?