I’ve played Dark Souls 3 a few years back and I remember there being a hostile NPC towards the end of the game who was a human female priest of some sort, wielding a scythe (or some other long melee weapon), casting frequent lightning attacks at me. She was wearing light armor, probably a robe and it was light colored. She had her own monologue during the fight, she was voice acted. She wasn’t a boss, nor a mini boss, nor an NPC invader. She attacked me instantly when I approached her. I only played the standard Dark Souls 3 game, not the DLCs. If I recall correctly I might have encountered her in Profaned Capital or a location similar to it. I think It was after a boss fight towards the very end of the game. I looked literally everywhere and found no signs of her existence so I might have gone crazy. Please help identify this enemy for me.
sounds a bit like sirris, but not all of it matches your description.
Check her out on wiki or youtube and see if it might have been her.
i dont think she attacks you though if you dont attack her first, but there are instances where you fight together. Wasnt at profaned capital either... so its probably not her XD but her questline has various ways to go about, and i could have simply missed the outcome you dexcribed...
otherwise she matches the description of feamle priest with a long melee weapon.