本句表示：她没有被晋升，但本应该得到晋升。用ought to + 不定式完成体。

She hasn't been promoted, but she ought to have. 等于：

She hasn't been promoted, but she ought to have been promoted.

不定式若用一般体 to be promoted，那么，晋升就是将来的事，后面的but 就不对了。

She hasn't been promoted, but she ought to be. 等于：

She hasn't been promoted, but she ought to be promoted.