Yeah, I was trying to figure that out myself when the mask really stood out to me. Did Dinah ever wear her mom's mask? That's usually the easiest way to tell them apart, in my experience. It's also worth noting that Miller tends to use the older versions of the characters, as evidenced by Barry!Flash and Hal!Green Lantern in DK2, when they were both still dead in normal continuity (though Dinah Lance being active at the same time as those two just confuses the issue further).
I really don't know, it's between the mask and the Ollie lookalike. Or the third and most likely option, Frank Miller screwed up.