I have tried to create an opposite hand mirror component in an assembly. I have broken the link to the original because I want to independently edit the mirrored part. Everything seems to be good, except for none of the datum planes were mirrored. This is problematic. When I examine the mirrored part's feature tree, the datums are recreated, but show up at the original location. So the datums are copying, just not mirroring. See attached example.
I guess this might only be a mirror of the solids. The sketches don't really mirror either, but copy as well to the original location.