She was forced into this her mother insisted on her doing so to restore the Ashford' name.
I think that Nina kind of put her back to her place with her harsh words .
I saw that Kallen was in next episode's cast I wonder how they will show it to us I'm thinking she might be wearing that dress as seen in the previous scans
Some people were talking about the Geass memory rewrite the Emperor might use on her but there are others ways to wipe a person's memories brainwashing/drugs can be as effective as well