If the company did not retain the information you are missing there might not be much that can be done. If this previous employee purchased the software herself and created her own account for the purchase/registration then it is possible your company has no right to it that they can prove.
Try serial number and activation chat support (non-CC)
http://helpx.adobe.com/x-productkb/global/service1.html ( http://adobe.ly/1aYjbSC )