Just catching up here so forgive me if this is widely known -- was the baby shown to be female by her doctors/through US at some earlier point? Otherwise, if her time with the newborn was so brief, and amidst such trauma, when was she concerned enough or able to determine its sex?
Using "her," let alone "Annabelle," just strikes me as odd under the circumstances described. This is a bit of a flyer, but it may be worth noting too that the name Annabelle has some connotations for teenagers post-2014, after that eponymous entry in the Conjurer franchise came out -- a doll, not quite human, with frightening powers. My kids, who are much younger, are actually uncomfortable just hearing that name after enduring all kinds of gory rehearsals of the movie in the school ground (as us oldsters might have been with "Jason" or "Michael Myers" or "Freddie Krueger")
Again, this is not meant to be a detailed theory -- just a few scattered thoughts.