[quote=@Rtron]
<Snipped quote by Hael>

And Vestec will stop by from time to time and add more and more corruption.

NICIEL CANNOT BE EVER VIGILANT ON SLOUGH. [@Scarifar]
[/quote]

It's true that Vestec can continuously try to corrupt her, but it's not going to be easy.  By trying to corrupt her in the infancy of her life, particularly after more benevolent gods beat him to the punch, he unintentionally inoculated her.  If not for Toun's gift of perseverance and its associated rejection of entropy, Vestec would have been far more successful.  Ull'Yang's gift has also given her a greater ability to recognize and resist bad influences.

Of course, Niciel's gift did not go as well as planned either.  Despite her good intentions, she did in fact 'force' her power on Slough like Vestec had done, and Slough resisted her as well.