Karin is a sensor so Mei's mist is useless and due to Uzumaki healing abilities, the mist's damage won't do much. Then while Mei is blinded by her own mist, Karin kills her with a kunai to the face.
Theoretically yes but I can find a loophole to that one as well.
How does Sakura beat Karin? Karin is a sensor and a medic so dodging should be second nature to her. Karin would eventually outlast Sakura.
Karin didn't want to fight Sasuke and was caught off guard by the chidori sharp spear.
Current Temari, probably not but Karin was definitely stronger before the War Arc though.
