Wow, 15ft back is a pretty fair reach for even the M3s. I've not seen M2s to compare size-wize with M3s, but they don't appear a heck of a lot smaller in the pictures, although they just might be!
One interesting point that might want to be addressed: Your explanation of her and her group make her sound, uh, perhaps a bit laid-back(to coin an oft quoted phrase) Seriously, is she more of a serious listener, or has she a more casual attitude toward her sound system? Hey, might make a difference.
As far as which would give the better sound, that's a tough call having never heard an M2, but with the experence I Have Had with the M3s, I can recommend them without hesitation. I don't have a bad thing to say about the M3s, and I've had them for the front three channels for quite a few years now with no complaints whatsoever. (Even liked them so much that when we moved into a new larger house, when it was time for larger mains, I fought back a very strong urge to go with M60s, but stuck with something I knew so well, the 'ol pleasant sound of the "laid-back" M50s.) Interestingly enough, in my room anyway, the M3s put the main performers at the plane of the TV, the M50s put them just slightly foreward!!! Yeah! I would call the M50s foreward!!!
But I stray...
Bottom line? No question any Axiom set up would be a vast improvement, but for the right individual, the M3s would be hard to beat.
Best of luck in passing along your recommendations, it ain't an easy task trying to think for someone else!!
(Some of us have enough trouble just thinking for ourselves!)
Rich.
