so, in season 3 of SPN, Kripke was forced to add more female characters (by the network) one of whom was Bela, a self-serving thief who was completely irredeemable - she shot Sam, stole from Dean, tricked Dean and Sam, sicked Gordon after Dean and Sam, killed her parents in a demon deal, stole the Colt (the only weapon to defeat Lillith) and tried to murder Sam and Dean in their beds.
Only in the last episode do we see any a tiny glimpse of backstory (that Bela was abused by her father and Lilith tricked her into a demon deal) but that is hardly redeeming, because she still tried to kill Sam and Dean to get out of her deal. She had no friends, no allies, no sympathy or compassion for anything but herself, only responding to threats.
Now season three was truncated due to the writers strike we won't know if she was going to really have some redemption, but Kripke never liked her character, and fans hated her so Bela got ripped apart by hellhounds (alas not seen)
and this has nothing to do about not liking female characters, or disliking the actress, it's all about how the character was written, so seeing Bela pop up in 'positive females in SPN' leaves me scratching my head, particularly when they leave out kickass allies like Linda Tran and Jodi Mills.