After being shot and paralyzed by the Joker in Batman: The Killing Joke, Barbara Gordon (Batgirl), now being a paraplegic, becomes Oracle. After some indeterminate amount of time, she is able to walk again and revives her old superhero persona, Batgirl.
When and how did Barbara Gordon (Batgirl) start walking again, and how did she revive her old superhero persona, Batgirl?