A hard reset might just do the trick.

Did the previous owner de-authorize the device from their Sony Store account? If not, that will also need to be done so she can purchase and load books via the Sony Reader Library. If she is able to purchase and load books via the Sony Reader Library then it must have been de-authorize. If she cannot, then contact the previous owner and ask them to call Sony Support and get them to de-authorize the device. Without the device the previou owner will have to ask sony to do he de-authorization.

Good luck and I hope she enjoys her reader!