The sadness was that they did not add the sequel addendum to her original contract. That is 101 for new stars.
The contract had the standard clause. The studio had to make an offer on a sequel. They could force her back to a sequel by simply paying a sensible market price for eighth banana in an ensemble cast. Paramount played her agent for a sucker, I strongly suspect, because Director Nimoy had already decided to recast. And to reconceive the character while he was at it.
I had read that they did not add that clause, which is pretty common, ask Natalie Portman regarding doing Thor 2. But I could be wrong.