Though Pedowitz might not have sounded too bothered by NK's 'letting the cat out of the bag' regarding her character's fate, I can imagine the producers were actually livid with her for not following proper protocol. As I mentioned before, actors sign non-disclosure agreements as part of their contracts that force them not to reveal plot points. Even though she was apparently let go and no longer has any real 'attachment' to the show, the NDA-type clause in their contracts can extend long past the time they get fired (just so they can't go out and gossip about the circumstances of their firing, etc.). In theory someone who does what she did could get sued for violating their NDA, but of course the NuDynasty producers likely won't do it because, frankly, the revelations barely caused a ripple on social media. If this had been Mary Crosby confessing in the National Enquirer that Kristin shot JR, that would have been lawsuit fodder for sure, but Cristal's fate hasn't been keeping very many people up at night in comparison.
Their parting of ways must not have been very amicable if she was that willing to burn her bridge, and she must have felt the chances of her being written back in somehow were so remote/unlikely that revealing the plot twist would have no effect on her being re-hired at some point. Kind of like calling your boss a $%^& in front of everyone when you quit, since you won the lottery and thus know you won't ever need to come back.