How is Daisy successful because of her KNOWLEDGE OF THINGS.

From the way you've worded your question, I assume your referring to Daisy's ability to walk away from Myrtle's death unscathed by guilt ot feelings of responsibility. We'll never be sure what Daisy's reation was post accident, but from Nick's accidental meeting with Tom on Fifth Avenue, we can assume she's doing just fine. Daisy's strength in knowledge comes from her understanding that her husband will never leave her..... they're an institution. She also knew that Gatsby, as well as Tom, would never let her take responsibility for Myrtle's death. She knew that both men would protect her and her reputation. Beyond that..... she would have seen Myrtle as a nobody, and her sense of entitlement combined with her wealth made her untouchable.