End of the day, we aren't ever going to be able to properly categorise companions until the DWU provides a proper, detailed and clear definition for what a companion is. All we have to do look at the Behinds the Scenes section at Companion to find how difficult our wiki has had defining the term.
Sure, we could take it on a case by case basis defining each character's legitimacy as a companion, but without the definition this is untenable. Only option I can see is to either a) go with a dictionary definition but that's far too restrictive for the show or b) simply leave it as is until a tangible definition is provided by the DWU itself. Granted, neither option is satisfactory, but then dealing with linguistics, semantics and definitions is never easy.
So, with that said, I personally do not see how we can properly and permanently resolve this case without a said definition.