Getting past activation lock on an iPhone 5, have original ID but account has been locked

My grandma recently got an older iPhone 5 from some friend of hers and asked me to fix it as it was disabled when she received it. I successfully reset the device using iTunes, up to the activation lock. I have the correct ID and a plethora of passwords provided by the previous owner, but none of said passwords worked, and now the ID has been disabled. I was able to ask her to use the email associated with the ID to re-activate the ID, but she has subsequently forgotten the password to that account as well, and can't seem to access the recovery for that email. After spending most of the afternoon in a goose chase, I'm at my wit's end. I've read on several places, both on and off of the official Apple Community forum, that Apple can recover the device if you have proof of purchase, which can be provided- I've also read that unless the previous owner is able to re-activate the ID, the phone is essentially an expensive paperweight. Any good advice on how to go about this?