The events folks are the ones who invited O'Donnell, and then, because of a backlash from the attendees, had to cancel her. They seem to be completely responsible for mishandling the event.
And if Palin also requested O'Donnell not be there, I wouldn't blame her. It seems obvious O'Donnell was just trying to use Palin for her own book promotion. I wouldn't take kindly to being used that way either.