Lady Susan is debating how she should punish Reginald, but her intended “punishment” rings false; even if Reginald were trapped in a loveless marriage with Lady Susan, it’s unlikely that he would view it as punishment. Lady Susan would, after all, want to control his finances—and in order to do that, she’d at least need to keep him happy. This is, notably, the first time Lady Susan has ever mentioned a potential marriage to Reginald; previously, she denied that she wanted to marry him. It’s possible that she’s framing the marriage as a “punishment” now, but she really intended it all along. This framing allows her to seem in control, even though she really needs Reginald’s money. In fact, her plans seem increasingly impossible, suggesting that Lady Susan is losing control—which would explain her sudden urge to get married. Sir James is gone (Lady Susan confirms that it was a tactical surrender), and forcing a marriage between Sir James and Frederica would mean going against Reginald. Meanwhile, Frederica loves Reginald more than ever, which is dangerous, since Reginald obviously isn’t immune to flattery. In order to marry Reginald
and punish Frederica at the same time, she needs to secretly force Frederica to marry Sir James against Frederica’s will, all while ensuring that her daughter won’t go to Reginald for help again. She can’t even stay with the Johnsons, since Mr. Johnson hates her. The scheme is therefore a secret operation, which certainly doesn’t imply that Lady Susan is all-powerful or even entirely in control.