With the last chapter we have seen these things about Mago, too:
1-] Not prime Mago's reversal has limits, it pushed Urek nonnegligibly, but still did not bash him to the walls, while Urek was definitely going for that.
2-] Similarly, after Mago made reversal, Urek attacked her with shinsoo, or light or whatever and Mago could not do anything. What I see is that Urek's attack was faster than Mago can react with her reversal or even dodge (maybe dodging was impossible against that wide attack, but still).
3-] Now we know why Mago even awakened herself earlier just to entice Urek. Since he is by far much more powerful than the lot around, turning his hopes into despair was the surefire way to improve her power. Although not that important, we also saw, again, that Maschenny co, Leo, or Asa or all of them's hopes to despair could not really hold a candle for Urek's despair here.
4-] She does not seem to make two different reversals simultaneously, so wide "not enter the castle" may be canceled each time she uses reversal for something else. Hence, i think there is no passive reversal skill.
The constraints:
-No multi simultaneous use
-Inherent power proportional reversal effect
-Hope-to-despair according to the despairing person's power, and proportional Mago power increase
-No passive use, hence Mago's reaction speed.