Trying to figure out the "surprise" in We Are All Completely Beside Ourselves

As M forewarned me, there is a surprise in Karen Joy Fowler's Booker-nominated We Are All Completely Beside Ourselves (what's this, a new title trend, sentences as titles? I find I can never exactly remember them) - so though I have read only the first 60 pp and have only my own guess as to what the surprise I may give it away so stop right here if that bothers you. In any event, I half figured it out before even starting the book (and no I did not read blurbs or reviews or jacket copy) - from the acknowledgements on the copyright page where Fowler thanks the Kafka estate for permission to quote from A Report to an Academy: K's well-known story about an ape captured and raised as a human who is speaking to an assembly of scientists. My first thought: the narrator's actually a chimp or an ape. The novel begins with her as an eccentric - very talkative child, now a student at UC Davis, kind of a loner, gets into a bit of trouble because of her impulsiveness, gets befriended by a very out-there wild woman named Harlow - but unless all rules of narration are broken she's obviously not a chimp. She tells us that her father - a psychologist at a university (Indiana) suggested she begin telling her tale in the middle, which she does, so not until about 40 pp in to we hear her back story, and that's when it became clear to me: she talks about being sent to stay w/ her grandparents and when she returned "home" the family had moved to a new house and her sister, Fern, was gone. So it appears that her father, a great experimentalist, was raising her alongside a chimp to see the effect on each other and on the family (there's an older brother). Well, you can certainly accuse Fowler of authorial manipulation - no narrator would tell her life story while artfully concealing the central point, but this is art and entertainment, not documentary realism, so I accept her playful narration - including her very appealing narrative asides to the reader and her general light but fast-paced narrative style. My guess is that the long-vanished brother - who seems to be looking for narrator near the Davis campus -- will reconnect w/ her and the two will set off, with Harlow, to find and to free the "sister" Fern. Though this novel isn't a documentary, if my suppositions are correct it seems to have been inspired by the recent documentary on families trying, with little success and sometimes w/ serious consequences, to raise a chimp as a child.