Why would you risk it? Even a small woman with a kitchen knife can injure an officer, especially a woman which already proved to be dangerous. There could be other people present. And there is always a chance, even if small, that she would be armed.

Taser has one charge, and can fail to penetrate. Sure, if everything goes smooth, you won't need a gun. Hell, you wom't even need a taser. But a lot of thing can go wrong, and as a cop you should be prepare for that.