In the episode Q Who, Guinan and Q encounter each other for the first time in the series, and it is obvious they already know each other.
Q warns Picard to get rid of Guinan:
"Picard if you have half the sense you pretend to have you would get her off your ship immediately. And If you like I'd be more than pleased to expedite her departure."
At which point Q raises his hand as if he is about to use one of his powers on her. In response Guinan adopts this pose:
Q continues speaking of Guinan:
"This creature is not what she appears to be. She is an imp, and where she goes trouble always follows."
This exchange between them raises various questions.
Did Guinan have any defensive powers against the Q's powers?
Q implies that Guinan was not who she appeared to be. Was the true identity of Guinan ever uncovered? Or is this more deceit from Q?
What was the prior relationship between Q and Guinan?
I am looking for any explanation, in or out-of-universe. I am guessing that originally they were intending for Guinan to have a certain back-story that was later abandoned by the producers - but this is just a guess.