It’s possible that even her parents believed that she went "insane" as Garam told us in Season 2. Her attacking members of the Zahard family and the rumors surrounding her going insane might have convinced them that it was too late to save her without risking everything. This could all be made up and they wouldn't be able to go against Zahard and the other Families.
We know that Gustang defected from the Zahard Empire. This decision could have been his way of silently opposing Zahard without directly challenging him when Anne was sealed. We also know that after Anne was sealed Blossom is now opposed to the selection of Zahard Princesses.
It can also be implied that the Eurasia and Bidau families' hostility towards one another stems from whatever happened regarding Anne being sealed. We know they have forbidden marriages between their two Families.
We know that Gustang defected from the Zahard Empire. This decision could have been his way of silently opposing Zahard without directly challenging him when Anne was sealed. We also know that after Anne was sealed Blossom is now opposed to the selection of Zahard Princesses.
It can also be implied that the Eurasia and Bidau families' hostility towards one another stems from whatever happened regarding Anne being sealed. We know they have forbidden marriages between their two Families.