It's been a long while since Aredhel spoke to any of her kin. Murdering your '''husband''' apparently makes family dinners awkward, and she hasn't had too many people who won't ask questions or side eye her about that since the Feanorians' final collapse. She prefers traveling, anyways, with Men or honestly Dwarves - Dwarves have a very finely honed understanding of sarcasm.
But she's heard rumors on the grapevine, of a rather dramatic scene at Ost-in-Edhil, where her cousin Celebrimbor apparently cast out a certain guest in a storm of fury. She's heard a variety of rumors about that guest, and, well. Aredhel has good hunches, and she's got a sense for what's going on. And she knows just what's needed after a bad breakup.
Namely: a large pack of very good wine; provisions and maps for a long trip; a new brace of arrows; and an extremely nice sword Aredhel stole from Maedhros before she could jump off a cliff with it (she usually wields the extremely nice sword that Turgon had forged for her, or preferentially the extremely nice bow the Feanorians gifted to her when she drifted into their crowd; Maedhros's old sword is an extra for special occasions).
Taking revenge on a lying, traitorous girlfriend who was possibly secretly a Maia is probably slightly different logistics than for a lying, traitorous husband who was definitely an elf (until Aredhel got to him, at which point he was a pincushion), but Aredhel is pretty sure they can improvise if needed.
She strolls right past the guards the city has hastily posted - they're overworked, and Aredhel could teach these whelps a few things about stealth - and right up to the headquarters of the Gwaith-i-Mírdain, then terrifies the first elf she meets (cowards) into telling her where Celebrimbor is.
Aredhel isn't stupid, and has timed her approach for when her hunch says her cousin is unlikely to be busy, but she still does knock before letting herself in. Once.