Character mistake: When Kathryn reads the journal copy in the final scene, the camera shows some pages she reads. At one moment, one of the headings reads, "WORLD OF FREINDSHIP".
Continuity mistake: The licence plate of the taxi which hits Sebastian in the end changes during the shot. (01:27:35)
Kathryn: So I assume you've come here to make arrangements, but unfortunately, I don't fuck losers.
Trivia: This movie is a retelling of the story of "Dangerous Liaisons."
More questions & answers from Cruel Intentions
Answer: Sebastian could have had a will and left it to her. Plus she was likely either in jail or rehab after being caught with cocaine, leaving her with little power to do anything about it.
LorgSkyegon