Guinan’s main “power” is convincing people of things by listening to them and chatting with them. I suspect she could just convince everyone to ignore Q, and that’s the last thing he wants.

It’s kinda like how the most powerful force in the TNG universe is Picard yelling about duty or the Prime Directive or something. He’s stopped Romulan warbirds in their tracks and the entire Klingon High Council (multiple times). He destroyed a Borg cube with a single word.

So much unrealized potential with the character…

Not yet