I think you have it right the first time around, but just to try and clear it up. Let me try another way

ME - SE Account, Registered via PC. My PSN account is linked to my SE account. (PC game copy from 1.0)
SIS - SE Account created via PSN and linked to her own PSN Account. (PS game copy)

Now when i try to play the game on PSN (In my PSN account) its not available for download, So that's why i asked if i needed to buy another copy.