Kamichama Karin Vol 3

Kamichama Karin Vol 3 by Koge-Donbo. A Fantasy manga rated Teen, published in English by Tokyopop in 2006.

Karin Hanazono is an orphan who's lousy at school and has just lost her beloved cat. Then she discovers that her late mother's ring can transform her into a goddess, and that a cool, arrogant classmate named Kazune knows a lot more about it than he lets on.