I'm interested to see what she means by "use the duke's wealth to swallow him". Is she planning to bankrupt him by this sort of extravagent spending? If so, that's a simpler revenge plan than I had imagined.
Leabic doesn't know what she's done. Telling an idiot, or someone playing an idiot, to check with you before doing anything can turn out very annoying. I imagine that our dear MC is going to completely screw up crucial situations because "she didn't have permission" to handle them at the time. The minute our MC shows her face in high society, she's untouchable to an extent. The duke can't just kill off the woman playing his daughter until the plan is over.