Ironically, Willy, who had a very questionable moral center before he was bitten, always seems guilt-ridden by what Barnabas is asking him to do. Carolyn, on the other hand, who obviously had a stronger moral center before she was bitten, follows Barnabas' orders without qualm or question. Of course, Barnabas hasn't ordered Carolyn to do anything on the order of what he ordered Willy to do (i.e., kidnapping Maggie, procuring blood for him, disposing of Maggie). Perhaps that explains the difference.
Also, Carolyn doesn't seem to be afflicted with the kind of feverish, enervating sickness that Willy and Maggie were after they were bitten.
Fantastic episode with great acting all around (especially NB).