theory: Aredhel was the most skilled among the Noldor at spells of concealment
support:
she was particularly friends with Celegorm, so it's reasonable to conclude that she, too, was a hunter. stealth is a valuable skill for a hunter.
why did a woman who grew so impatient with Gondolin that she badgered her brother for years into letting her leave, and then slipped away from the escort he insisted upon, even move to such a secret city in the first place? Because she's the one who helped hide it in the first place
seriously, someone in the building of Gondolin must've been an expert at concealment spells. Even with Ulmo's blessing, you simply can't build and move en masse to an entire city without anyone finding out where it is without serious juju. why not Aredhel?
Turgon let his sister leave Gondolin on vacation when he never let anyone else go not out of weakness to the pleas of family, but because he knew that if Aredhel didn't want Morgoth or his spies to see or track her, they fucking wouldn't see or track her - and if they could, Gondolin's hope of secrecy was lost anyway.
alas that Eol was even better at it than she was (maybe this intrigued her at first. maybe there was delighted hide-and-seek beneath the dark trees before there was only hiding)
alas that she didn't have time to teach Maeglin all she knew