So we see on page 12-14 that maou isn’t useless, I’m guessing that thing she stoped was the spirit that told magical girl to attack them.
Hell with the way they act I’m wondering if they aren’t actual demons but confused shrine spirits
I think people have the wrong impression of maou. She stopped the shiny thing that was clearly going for magical girl. I believe the implication is her plan is to stop that creature and she lived with magical girl because she knew it would go after her.