Well in my case, PA didn't get any email either.. First I got AOR email, then I received another email on behalf of PA with pdf file asking PA to link her paper application to online account. And then third email as a confirmation of linked account. PA haven't got any email. Because we submitted "Authority to Release Personal Information to a Designated Individual (IMM 5475) " form along with application which basically makes me authorized person for PA's application.
You can link the file wherever you like as far as you put details of PA in required field. I have used my old user id password but filled details of PA while linking paper application. Also I used Last name and File number to search the file and then linked..!!