This about how the FL's mother met the FL's maid Anna at the ball and said she only came bc she wanted to talk to Anna. Then Anna is seen giving FL a cup of tea and FL says the tea tastes different than usual and it has been sometime since she tasted tea like that.
There is a spoiler that the FL is sick and her mother kept adding some medicine to her tea. The medicine is rare and only the Empress can give access to the medicine to the FL's mother. The Empress put a condition that FL has to marry her nephew if the FL's mother wants to keep recieving the medicine.
I don’t understand the purpose of not telling your very intelligent adult child that they have an illness.