It is an open-voiced jI minor seventh chord in third inversion, or an open-voiced JI major added sixth chord in second inversion. So, in a sense, Margo agrees with this model tha this "added sixth" chord is the most concondant tetrad with distinct pitch classes, though perhaps not in the voicing she whould have suggested (of course, had I perhaps increased the upper bound for adjacent intervals, some other inversion of this chord, or some other chord, might have come out as most concordant.)
