Willow does not have long to improve the Wards, that “clamp down” upon her Witchcraft, as her magic is soon required to assist Buffy: raising a “force field” (to help keep an “Uber Vampire” at bay), performing locator spells (to find other potential slayers, before The First can eliminate them), reopening a space/time portal (after Buffy jumped through one) and using a crystal/charm (to help a reformed Andrew remember more about The First).
The final test of Willow’s reformed character occurs when Buffy asks Willow to change the “Slayer” spell: so that all potential slayers shall have the same strength as Buffy (and Faith). Willow is initially scared by the request, as she believes the spell could take her beyond Evil Willow: into a total loss of self control. Fortunately, this turns out not to be the case: and after researching the spell, she is able to cast it with the help of Kennedy (a potential slayer), resulting in Willow glowing in white (and thus being equated with a Goddess). After the “Slayer” spell is successfully cast, Willow collapses from exhaustion; but is able to savour the fact that she has helped to defeat The First, and in doing so, has fully redeemed herself.