Katara should have practiced bloodbending more

As we see with Amon and his family in TLOK, with enough talent and practice bloodbending can be used without a full moon.

Katara is probably the most talented waterbender we see, able to learn bloodbending almost instantly and a master of water bending in a few months. If she put her mind to it she could have learned to use it without the full moon, especially after she found out it's possible from the courtroom attack.

Bloodbending is seen as a bit of a horrific ability, so she may have some moral opposition to it, but it can be used in much different ways.

As a healer, bloodbending would help immensely. Able to stop bleeding, close wounds, and even potentially reinsert blood. Not to mention things like directly pumping the heart and even purifying blood by directly removing bacteria and such. Also she would have been able to reverse Amon's bending seal without Korra's deus ex machina.

Even in combat it could be useful without bending other people's blood. You could bloodbend yourself to allow flight or increase the strength of your muscles.

With her existing skills, bloodbending would have made katara the most powerful non-avatar by far.