PS3 Digital Upgrade Service question

I really hope I am posting to the right forum. I don't really think this is a technical question but its the only one I see fitting and search didn't help me either.

I have a friend that won't buy Heavensward unless she can get the Griffin mount. I told her that she can just buy the game and then do the digital upgrade to get the CE content. She doesn't believe that will work though since it is on the PS3 and not the PS4 or PC. Can she do the upgrade? I keep telling her she should be fine but she wants to see some confirmations.