Conversation so far:
what was imperial by Cassandra Nova?
Angered at Cassandra Nova's treachery and realizing the danger she posed, the Imperial Guard fought Cassandra, who defeated them and headed into the mansion.
what was the imperial guard for with Cassandra Nova?
The Guard with Cassandra Nova fought the X-Men until they were able to show the truth to the Imperial Guard.
was this successful when the Guard fought the X-Men until they were able to show the truth to the Imperial Guard?
Cassandra Nova's essence entered the body and was locked into a self-repeating program in the synthetic brain.

Question: what was her greatest accomplishment?
Self-contained rewrite: what was Cassandra Nova's greatest accomplishment?