I have to be honest, Brooke has never been a favourite character in the Under the Never Sky books. Continuing with the honesty, this novella hasn't endeared her to me. Obviously I bought the novella for the sneak peek at book 3. Of course I'm now kicking myself for reading those three chapters now because I've still got two months to wait before I can get the full book! 
 The novella focuses on Brooke and her decision to move on from Perry (since he's chosen Aria over her). It starts with her feelings of rejection that she's reflecting upon while tending to the Dwellers - who all appear to be ill. Then she decides that she's going to move on. Only I'm not keen on how she goes about it, but commenting on it would spoil it. 
 The big difference between Brooke and Roar and Liv is that the events in Brooke are going to be relevant in Into the Still Blue, whereas those in Roar and Liv were simply a look into a favourite character's life before the events of the trilogy even kicked off. 
 It's a novella that's relevant, but not about a character that I can get enthusiastic about.