I don't think that Buffy never warmed to Faith. I think that she did feel an affinity for her between Homecoming and Revelations and it was Faith who pulled away from her after Revelations. The two become close again after Helpless and The Zeppo. After Bad Girls Buffy just wants Faith to own her shit which she's too damaged to do at that point.Buffy definitely had every reason to hate Faith after everything Faith did in Season 4 (and after she crossed over to the Dark Side in Season 3) but I kind of get where @Btvs fan is coming from. Buffy disliked Faith from the moment Faith showed up and she never really warmed to her. Whether it was a territorial thing (Buffy does seem to clash with other Alpha personalities, hence why she and Cordy were never close) or just a personality clash, she was pretty open about her dislike of Faith. They never really became close and Buffy never seemed to put in the effort with Faith that she did with other characters.
So while I do think that Buffy was justified in her reaction to Faith in Sanctuary (while simultaneously thinking that Angel was right in his actions to stop Buffy from getting revenge) I also do think that Buffy was always written to dislike Faith, which does make her hatred of Faith later on a bit tainted (or rather, not always about what Faith did to her, but instead rooted in a previously unfounded dislike).
The rest yeah I disagree with Buffy but I understand why she thinks like that.