When Emily called Lorelai out about Luke during a FND, she followed up Lorelai’s admission with “What in the world are you thinking?” She’s always been against Luke and even her Romanoffs comments weren’t acceptance, merely acknowledgement.
I think Emily was a product of her situation in life. It couldn’t have taken long to find out how much Trix hated her, and later to have only one child and no male child to inherit would have displeased Trix even more.
I can see but not excuse that Emily would throw herself into her job of corporate wife and society mother, but become bitter and cruel when it wasn’t the 1950’s version of happily ever after.