Holly Marie Combs reportedly thought Billie was beyond redemption after everything she'd done and wanted her to be vanquished in the finale along with her evil sister, but the other producers disagreed.Gojirob said:
Billie hating the Three was done so poorly, it almost negated pitying what she had to do at the end.
Still, I don't know what HMC's personal feelings towards Kaley Cuoco were, but in the final episode it's manifestly clear from non-verbal cues alone that Piper absolutely loathes Billie, so she at least got that much of her view into the show! (Incidentally, the scene in the penultimate episode where Piper punches Billie in the face and then tries to strangle her was my biggest "Hell, YEAH!" moment of the entire season.)