Thee other possibility is that the Board told her to do something that she refused to do. If enough Board members felt strongly enough about whatever they were asking of her, then they decide that a paring of the ways is best for all concerned.
I would take her at her word that it was not for “cause” and therefore not something egregious. It might just boil down to an issue that she and the board didn’t see eye to eye on. Not on the same page. Which is a problem. Happened to a friend of mine.