Episode 17 sort of encapsulates it best since it's a huge character shift scene so "flirtatiousness" would mostly be "an increased willingness to invade personal space" as exemplified by how she doesn't hesitate to take the eyeglasses off an ambassador. It's an increase in confidence and risk-taking. As for the intelligence bit, yeah political skill would fit the bill along with having a lot more stock knowledge to break the ice (e. g. Episode 11's episode in Moscow shows her lacking in grace when dealing with the guests at Marquis Weridge's party which contrasts how she better mingles with ambassadors later on in the show. For better mingling, you have to know shit like "Oh right, your homeland. Awesome place. I hear the GDP is blah blah blah pretend I care.").