To have been trading blows at 10c for even a minute would entail (nope, not gonna calculate this one) probably something like millions of punches/kicks/etc...of course this also ignores relativistic problems, let alone ignoring what limitations have been set for the characters previously (so much for Mach 10 or 21 or even Mach 10,000)...just to be able to "see" heat vision coming implies that Diana is using some kind of superluminal sense, since the light from the heat vision is moving no faster than the beams themselves.
If this is the case, then Diana is not limited to Mach 21, and, well, so much for trying to minimize collateral damage.
In which case we can readdress the topic of this thread: can Diana react faster than the nerve impulse in her opponents can move? If Juntai is intepreting the Earth-bound fighting correctly (and I will give you that benefit of the doubt, since I wasn't there), then the answer is yes. In fact, if Diana can fight even at just lightspeed, no one but Superman or the Flash could tackle her.
In fact: since Diana is based on magic, one could argue she is immune to relativistic effects, while Superman is not.
Well, DC, put That in yer blender and puree..