It sounds like they might have installed it under an admin account, but then did the "JUST FOR ME" installation on it. Easy fix for them might be to go find the "COBie Extension.addin" file under the admin user account folder which is usually here:
C:\Users\<<admin login>>\AppData\Roaming\Autodesk\Revit\Addins\2015
and move that .addin file to the spot for addins for all users which is usually here:
C:\ProgramData\Autodesk\Revit\Addins\2015
I say "usually" just in case you have some PC configurations that are not right. Also, not the "2015". Just change the year for the version of Revit.
As a side note - I would also make sure you got the latest version from here:
http://www.biminteroperabilitytools.com/cobieextension/
The link on the autodesk.com page seems to be out of date.