Anna seems ambitious and quite devoted to the Wizard. Determined to be her own woman, she ensures the Wizard she will not spill his secret to anyone, not even Glinda. This eventually lands her in jail.
The Wizard releases Anna from her cell and takes her to Nimbo, where she investigates a mysterious portal and is injured in the process.
The Wizard seems to value Anna's expertise much more than he does Elizabeth's and decides to promote her to his chief advisor. Before that can happen officially, he learns that all the women in his Council has been spying for Glinda. Feeling betrayed, he shots Anna dead with Dorothy's gun, thus killing the only person in the Council actually faithful to him.
Anna was the only member of the Wizard's Council unaware of her true mission: to learn the Wizard's secrets and report them to Glinda.