All of Karin's special abilities seems to derive from her excellent control of chakra. However, her level of control can be even unique. She can detect others' chakra, transfer her own chakra to heal others, and conceal her own chakra from others. Although she has avoided most battles thus far, as a former guard to one of Orochimaru's prisons she is presumably a capable battler, as evidenced by her effortlessly taking down a prisoner attempting to escape.
Karin's special ability, the Mind's Eye of the Kagura, allows her to track specific individuals through chakra, seen when she is able to discern that Jugo is not among a crowd of prisoners through the standard concentration pose for molding chakra. It also allows her to pick up chakra from long distances, and notice changes in an individual's chakra. Kakashi Hatake surmised that Karin is a particularly skilled chakra-sensing ninja, as she is not only able to tell that his group is approaching, but can also sense how many of them are present, and that one is a dog. Karin's senses can also tell when a person is lying from the fluctuations in that person's chakra made from dishonest emotions.
Karin also has the ability to heal others by letting them bite her and suck in her chakra.[1] However, it is dangerous for her to use this ability more than once a day. It should also be noted that she had other bite marks on her arms, chest and neck which she wears long sleeve shirts to cover up, suggesting that she has used this power repeatedly.
It is said that she has the ability to completely suppress/hide her chakra from detection.[2] However, doing so will render her unable to use chakra, thus disabling her Mind's Eye of the Kagura technique.