The fact she becomes visible injured, limping and yet still continues to fight. Even before I knew anything about the lore, that made me feel really bad for killing her! It’s even worse when you know the lore.
As for the ring, in my game there was a message saying “Ring needed” or something similar at the site in question, and I’m pretty sure I learned of its location from someone in this thread. I guess you can piece it together by reading the ring’s description, but if you didn’t have it then I’ve no idea. Maybe there’s a vague clue somewhere, but it’s not like Dark Souls to ever spell anything out for you!