The following FAQ is taken from The) Unofficial FAQ on the CardgameDB forums:
What does Catelyn Stark prevent?
Since Catelyn Stark prevents opponents from triggering card abilities, she does not prevent occurrences mandated by the game, like "Forced Reactions", "Forced Interrupts", and "When Revealed". Likewise, as she only affects card abilities, she does not affect duplicates - which are defined as a triggered game ability. Finally, she only prevents triggered abilities, so she does not prevent anything that lacks a boldface precursor (e.g. keywords like Ambush or Renown).
However, she does stop pretty much everything else - including events. Since the limitation Catelyn is placing is on the player, not the cards themselves, she's not "restricted" to only affecting cards in play.