Hi, Cerridwyn. You might get a better response if you can post some more details. For example, what kind of computer does she have?
Did you deactivate your 700 from your accounts before you gave it to her? She might want to try a hard reset of the ereader if she wants to link it to her own ADE and Sony accounts. See this link for instructions. A hard reset will basically restore the 700 to factory defaults and will erase all content (like when it was new out-of-the-box). Then she can register it to her own accounts.
https://wiki.mobileread.com/wiki/Sony_Portable_Reader
EDIT: Looks like SeaBookGuy and I had the same thought at the same time!