Because I seem to be asking questions about all the Princesses - why was Twilight the only one to notice her odd behaviour at her wedding? Surely all her closest friends and relatives would be present? That is, if she had any.
@Latecomer
She might not have any. Even then, the ones that were there may have thought she was simply angry over the stress of planning out the wedding.
@mjangelvortex
True. But given how personable she is, to reach marrying age while having so few ponies who know her well is notable. Even Celestia was fooled.
@Latecomer
Some people act completely different when stressed. It’s not too farfetched of an idea for me to believe that they just made a mistake. Also, out of the Mane 6, only Twilight knew her. So that explains why Chrysalis was able to fool the others.
@mjangelvortex
True. But it’s still incongruous enough for me to make it a foundation for her backstory. (Along with other questions like, where was she before the wedding ep?)