In the first Dark Souls, when you enter Quelaag's Domain she attacks you without any discussion or trying to know why you have entered there.
Her sister, however, shows no hostility and neither does her servant, even though you killed Quelaag.
So why would Quelaag be hostile at first sight, and doesn't try to know if you came there to help her sister and give her humanity? Does she have any reason to attack the player instantly?
Any item lore or suggestions are appreciated.
Best Answer
There are several valid guesses as of why Quelaag is hostile from the get-go:
Quelaag's sister - the Fair lady - is blind and weak. Spoiler:
Lore-wise, the Fair Lady was transformed into the spider thingy by the Flame of Chaos incident. The reason to why she is weakened (and thus protected by her sister) is because she's attempting to cure Blighttown by sucking up all the blight (Eingyi being one of those whom she helped).
She and Quelaag were two of the only three (the third one being the witch Quelaana who managed to escape with no mutations) whose sanity survived the Flame of Chaos incident that mutated everyone else into demons (as their torsos are still human, so are their minds).
And you killed her sister to ring a bell, and now she's all alone with nobody to care for her, you monster.
For further info and clarification, refer to articles on the Fair Lady, Quelaag, and Quelaana on their wikidot pages.