I ran a Mac-like Linux distribution on her Linux PC, but it was not 'the real thing'.
I doubt you found something that's actually Mac-like. For example, did drag-and-drop work reliably between any arbitrary pair of applications? Did all of the applications support scripting remote? Did it have a system-wide search that did full-text indexing of all document types (including PDFs, office documents, and so on)?
Most such things are really crappy copies because they only duplicate the superficial irrelevant crap. I don't care if it looks like OS X - Apple's made a bunch of poor design decisions there in favour of good demos at the expense of long-term usability and it would be easy to improve matters. I do care that the core functionality works. Unfortunately, GNUstep has nowhere near enough contributors to be able to do a good job.