What is revealed about Daisy's character when she offers Tom the pencil at Gatsby's party? Has she undergone a change?

Daisy has, by this point in the novel, been reunited with her long-lost love, James Gatz--ahem, Jay Gatsby.  Tom has been having illicit affairs literally since their honeymoon, during which he embarrassed Daisy by having a car wreck with a woman (a little foreshadowing, perhaps?) that ended up in the newspaper.  Now that Daisy has newfound security with Gatsby, she feels confident enough to sarcastically offer Tom a pencil--a gold one, symbolizing the fact that he can keep his money, too--when he says he wants to go over to another table to finish dinner during Gatsby's party.  In this way, Daisy lets Tom know that SHE knows he is going to flirt with or perhaps even pick up another woman.  She even provides the means for Tom to write down her number or her address.  With Gatsby by her side, she no longer feels the need to tolerate Tom's emotional abuse for the sake of his social status and money.