Think again. Nagato's words 見え imply that she's waiting for the panty flash to happen.
True the 見え imply her noticing the flash, but her smile/slight blush was after Suzukaze's "Teyandei" and start shooting again. And 見え could be in "I can totally see it, be careful" too. Nothing can be said with just 見え.
More likely IMO is that she's often depicted fighting mainly with her sword rather than her guns. Depicting her as being a poor shot (but a good swordfighter) is the next logical step from there.