Becky has always taken bold moves for the chance to attain wealth, and so in many ways, her descent into gambling addiction is a logical evolution for her character. As he has sometimes done in the past, the narrator is deliberately vague about the details of Becky’s life, perhaps to capture how Becky herself can bend the truth, even sometimes when confronted with direct evidence against her (like when Rawdon walked in on her and Lord Steyne).