Tumblr's obsession with Heathers fueled this particular rumor mill for quite a while, so I would take everything with a very big grain of salt. But I heard that several accusations of diva behavior and a couple of things about performing whilst drunk were big causes. Never heard the playing hooky thing, but it could easily be true.
It's a shame though. I thought Barrett really carried the show and elevated some of the weaker parts of the material (when Heathers works, it works. When it doesn't, it falls flat on its face). Clearly she's not having any trouble finding work, and I'm very interested to see how she does with Sally Bowles, but I sincerely hope she has become more professional following the Heathers debacle.