Characteristically, we're told that Kitty "smiles and simpers" and hopes her turn to be engaged will come soon. She asks for balls to be held at Netherfield -- probably in furtherance of this goal -- while Mary wants to use the library. I can only imagine their reaction to Lizzy's engagement to a man who has a grand estate with a library that has been the work of many generations.
And now Kitty gets to spend a lot of time with her well-married elder sisters, and Mary gets to socialize without being compared to the prettier girls in the family. I like to imagine that Kitty and Georgiana became friends, and I wonder if Mary wishes she had not spent so much time shut up with her books!