We need to have at least two or three episodes to see how much Viv will allow Charlie to go full demon, and under what circumstances.
That aside, I think she's fine being in Hell as a 'natural denizen', but she knows that the souls that live there are unhappy. Also, I think the premise is that 'redemption' is possible, just very rare, thus the episode-to-episode conflict. We haven't seen it yet, but you can see from how they're setting up certain characters that this is the case. Serpentious calling out for his 'son', Angel Dust clearly having some remorse from time to time, etc.