Ah, yes. But I think Joyce was the mother and Dru was Joyce's girlfriend...Anyway, I really liked that story. It is:
[b]In The Shadows With Me by megan_tam_/b]
http://www.sweet-temptation.net/viewstory.php?sid=36Summary: Sometimes even the brightest light can't penetrate the darkness.
After years of unbelievable abuse, a broken and battered Buffy is finally rescued by her Knight in Shining Armor, but will their unique relationship and his boundless love be enough to save her?
Warnings: Character Death, Child Abuse, Extreme Language, Rape/Actual, Sexual Situations, Taboo, Torture, Violence