To me, this seems more likely to be the real reason that her contract wasn’t renewed, not that she’s just been “dumped” by VS. Those rumours were probably only created because nobody had provided a reason as to why her contract wasn’t being renewed. And to be honest, it does make sense that she doesn’t have the time to commit to VS, she’s incredibly busy and said a few months ago that her year is already entirely booked. If VS really didn’t want Miranda and had “dumped” her I suppose they wouldn’t have invited her to walk in this year’s show. But who really knows?
(Also read this article.)