She's peerless as a singing actor, and dedication to her craft, but perhaps one of the most difficult people to work ... with and around ... in part due to her painstaking attention to detail, and the snail's pace of her process. Yes, apparently she almost physically harmed Linzie Hately in CARRIE, in the now infamous punishment sequences. But Hately defended Buckley's work, actually, while admitting it literally hurt to do the show with her.
But from many sources, including a couple who've worked with her, I've heard it's her meticulous preparation that makes her "difficult" more than her diva antics. Buckley is notoriously slow, too, not wanting to lock in her performance until quite late. That may have worked for the Moscow Art Theater, but it's hell for a modern, efficiency-dictated production schedule. TV, notoriously fast, requires actors to arrive on set with performance-level work accessible. Perhaps Buckley's intense rehearsal demands, etc., are more the culprit than any show of 'ego.'
"I'm a comedian, but in my spare time, things bother me." Garry Shandling