Don't know it's simple to say that Karin's character is just to obsess over Sasuke. Right now one can assume the attack scared her immensely and jumps from one extreme to the other. If this is true then what's the reason for it. If anything even thou her allegiance to Sasuke is related to her feelings for him why this much exaggeration.
It could be interesting to be revealed that right now sasuke is in the good and doesn't emanate any evil chakra so she is fine and attracted to it, but probably when he will show again his evil chakra maybe things will change.
There's also the possibility that she will be used as a negative role model for Sakura and Ino. the placement of this characters and the fact that they are acting in support for the fight may trigger some conversations between the 3 of them. But don't know it would feel bland. If that's the case then Kishi would be ruining an interesting character.