I think that she could beat the Avatar and pretty much anybody.

bloodbending can only be used under the full moon.

yeah, true true, blood bending does only work throug a full moon, and if the Avatar is in any iminant danger he goes Avatar State then I dont think she has much of a chance.

did you see what he did to the fire lord kat. loses badly

She COULD beat him, even without any form of blood bending.  Technically she could freeze a charcter into a block of ice, and have the character's body shatter completely, in effect killing that person.  Katara does THAT and there is no more Avatar.

However, Katara is too soft in regards to her friends to do such a thing, so she would not even bother.

That and Nickelodeon would not approve of children seeing people's bodies shattering into ice crystals.

Neither one would ever fight each other but if they hypothetically did Aang would win. If he wasnt in the Avatar state it would be a decent fight but if he was he would beat her down.

Avatar would win. Any avatar would. Even if his water bending is not as good as Kataras yet it will be better when he is older, plus he can bend three other elements than she can. Also Avatar state, hello!  Any Avatar owns.

As much as I love Katara she would loose agains THE AVATAR......Ang in The Avatar state is so powerful that he can bend all elements at once....I doubt that Katara can handle Earth,Fire,Air and Water coming at her all at once...She's powerful b t not that powerful....

It depends on the Avatars skill level. If the Avatar learned to bloodbend she'd lose a significant advantage. 

" @Slight: Yeah but in one episode she blood bended a fire nation general in broad daylight "

If the fight is in character, there's no way she would use bloodbending on Aang. That's really the only shot she has of winning and even then it would be tough.