I was right (for a change): Guessing the surprse in We Are All Completely Beside Ourselves

Readers will see that I was right (for a change - I still remember how I completely mis-predicted the plot of The Woman Upstairs as I was reading the novel, though I also still think my plot would have been better) that Rosie's sister, Fern, is a chimpanzee; we learn this about 80 pages into the novel, We Are All Completely Beside Ourselves. As K J Fowler's narrator - I think her name's Rosie? - writes, she expected some readers to guess this salient fact somewhere along the way. She also realizes her readers will be, as I was, a little annoyed at her withholding this information - her narrator is very realistic and conversational, feels much like a new friend telling you her life story - except that it's pretty much inconceivable to me that she could or would withhold this fact: I can imagine telling your life story, up to a point, without ever mentioning your sister, Fern - but if you do mention her, as R. does numerous times, you can't not tell her that she's a monkey for crying out loud. Anyway, Fowler makes the best of it, has her narrator explain that she's sick and tired of having this family fact be the dominant chord in the song of her life. I can accept that, to a degree - and am in any event willing and eager to move along with this novel, as Fowler's narrative voice and sharp wit have kept me fully engaged. Shall I predict more? She's made it clear that Fern is still alive (it's about 15 years or so since she was removed or exiled from the family); we also learn that the long-lost brother has also tried to find Rosie; we also know that Rosie chose, oddly, to attend UC Davis because she'd heard that her peripatetic brother had settled there for a time: my guess is that the two will get together, along with R's new friend the adventuresome Harlow, and will "free" Fern from captivity. We're not sure, yet, and maybe never, exactly what R's father the psychologist was trying to prove or study by including a chimp in the family - but the strong fraternal (or sororal?) attachment R still feels from Fern suggests that the experiment was a success on some level: hers is not the kind of attachment one would feel toward a beloved pet, but true sisterly longing and affection. On the other hand, there have to be reasons why Fern was abandoned: violence, destructiveness, or something else? (Hard not to think of the horrible story of the chimp mauling in Conn. - these are still wild animals, strong and unpredictable. There's reasons why we have not bonded over the millennia w/ chimps as we have with dogs and cats.)