Was she using her own Apple ID on her old iPad? If so, restore the iPad again, setting it up from her backup. Do not at any time enter your Apple ID and password during the restore process beyond using it to authorize the erasure of the iPad. When the erasure is complete, have her enter her Apple ID and password whenever prompted during the restore and setup. As long as she was using her own Apple ID and password on her old iPad, this should ensure that your account is nowhere on the old iPad.