So I'm writing this novel, wherein my heroine comes back from the post-apocalyptic future to assassinate a guy in 1898 England and my hero, for his own reasons, is teaching her how to fit into society so that she can do so At the moment, we're on dancing lessons/ballroom attire. The people In The Know are the hero, the heroine, and the hero's sister.
1) What dances would be considered absolutely vital for Heroine to know? How many people need to be present for her to learn them?
2) If these are multi-person dances, how common would it be for an adult woman not to know them? Because if the hero has to, he'll involve the servants for the other bits.