Her internet beatdown of Dave Sim asking him to philosophically defend his anti-feminism. Which he failed to do.
She also had a light-hearted, far more friendly beatdown towards Jim McCann, then-writer of Hawkeye and Mockingbird, based on who would win in a fight, Dinah or Bobbi. Neither technically won, but a mutual CMOA between the two.
When news of the reboot hit, reaction was mixed to say the least. And when it was announced that Barbara Gordon was taking the mantle of Batgirl, it didn't make things better, especially with fans of Babs as Oracle, the mantle she had held for twenty years as a handicapped character. This really struck a chord with Jill Pantozzi of Newsarama, who like many disabled comic readers, viewed Oracle as one of the best positive examples of those with disabilities in fiction. Jill wrote a strongly worded response to the announcement to show how hurt she felt by the news. Gail read the article and was so touched, she contacted Jill and gave her the first interview on Batgirl and directly addressed fans' concerns. Let it never be said that Gail doesn't care about her fans in the slightest.
Offscreen Moment of Awesome: Two weeks after announcing she'd been fired as writer of Batgirl, she announced that she would be the new writer of Batgirl. We may never know how she pulled that off. In fact, almost certainly won't, because Gail Simone is much too classy to burn her professional bridges.