dont worry about it man... My X was 6'2"... I am 6'2" yet she was like 1/2 an inch taller then me (I think she was closer to 6'3" and just claimed to be 6'2")... she had a hard and fast rule that she would NEVER date a guy who was shorter then her

right... you can overcome most of these things like this by simply ignoring them and proceeding like it doesn't matter. The natural order of things is that the man leads and the woman follows (think dancing not teaching)... if you don't worry about it, she will follow your lead and not worry about it.
Oh and if this was directed at you... it's probably because she figures your about 5-6 inches taller then her, alot of times women arent as precise with things like height calculations... and if your really 4 inches taller she may see you and think your 5-6 inches taller