It might have corrupted <PERSON>, and she was already weakened anyway
The Avatar wiki page on energybending (the method by which it is possible to remove someone's bending abilities) has a "Dangers" section, which says:
Energybending is an extremely powerful and potentially dangerous technique. If the bender's spirit is even slightly weak, or bendable, they will be infected by the spirit of the one they are bending. As a result, the bender can be corrupted and even destroyed.
We see this in Avatar: the Last Airbender; when the lion turtle first teaches <PERSON> energybending, it warns <PERSON> that his spirit must be strong in order to not be corrupted by the other who's bending it being taken away.
Lion turtle: To bend another's energy, your own spirit must be unbendable or you will be corrupted and destroyed. (from Sozin's Comet, Part 4)
In the last episode of Avatar: the Last Airbender, we see that <PERSON>'s corruption nearly takes hold of <PERSON> as <PERSON> attempt to energybender his bending away, but <PERSON> proves stronger is able to do so without being corrupted.
... <PERSON>'s energy begins to make its way to <PERSON>'s body, consuming the blue and replacing it with red energy. Cut to a view above <PERSON> looking down at his face as the energy reaches his face and continues to cover the beams shining out his mouth and eyes. Cut to a side-view as the red light begins to take control and the blue light diminishes. Cut to close-up of <PERSON> as the red energy has taken over almost completely with just one eye left. 722
The blue energy begins to disappear, but at the last second it blasts out of <PERSON>'s eyes, overwhelming the red energy in the process and proceeding to take over <PERSON>'s own body. Cut to a wide shot of the area as <PERSON> completely takes over <PERSON>'s energy and an intense beam of blue energy erupts into the sky... (from Sozin's Comet, Part 4)
Part of <PERSON>'s character arch is that she is, unlike <PERSON>, far less spiritual. She might not trust herself to be strong enough in spirit, especially compared to someone both very spiritually strong and also corrupt (<PERSON>). Previously, <PERSON> had only used energybending to restore people's bending (and even then, it has just been "blocked by <PERSON>", not actually taken away via energybending).
Also remember that at the end of Book 3, <PERSON> is not exactly at her strongest, having been poisoned, so that's another reason why <PERSON> might not have been too keen to test herself. She is shown to be rather weak in the last few minutes of that last episode of Book 3:
<PERSON>: [Side shot, revealing <PERSON> in a wheelchair.] You know, nobody expects you to bounce back right away. It's only been two weeks. You need time to heal. (from Venom of the Red Lotus) 722