Hi everyone. Here’s my bonkers theory that ties in a couple of others:
‘So thats who’ does refer to the girl in the shop, but the girl in the shop is actually the doctor who has regenerated as female in the anniversary special (which would be SM’s: ‘change the course of who forever’, ie, the first female doctor) and so goes back in time to make sure that Clara gets the phone number for the tardis so she can call the doctor in BoSJ, and this is in the book which is written/updated by the tardis (maybe) who is leaking the past and future and hence knows the faces of the future doctors.