I don’t know why but i have a feeling that Sally may of started of slightly like Molly (but a lot more of a bitch ^^), she had a crush on Sherlock he turned her down in his Sherlock fashion and that eventually lead to her being with him like she is now.
I say this because, one Sherlock refers to her (although rather sarcastically) as an old friend - assuming the sarcasm was meant for the friend part, this seems to suggest they have known each other for some time.
Secondly Sally’s hatred for Sherlock seems way out of proportion for someone who is just jealous of him for his intelligence. I mean although justice isn’t really his motives all he had ever really done is help Scotland Yard solve cases and while people must find his ‘smart arseness’ annoying Sally’s dislike towards him seems a lot more personal. She constantly tells Lestrade he is useless to them despite the evidence to prove otherwise. Like she just wants rid of him. A consistently calls him a freak in quite a viscous fashion. Even Anderson’s dislike towards Sherlock seems a lot more ‘tame’ than Sally’s.
Although there are odd times in which she seems quite playful with him, even when she calls him a ‘freak’ - maybe this is the old feelings she used to have for Sherlock coming through slightly.
I could be way off the ball about the crush thing, but i still feel there is something different about Sally’s hatred to Sherlock, like she knows something about him that has personally offended her in some way. Perhaps he was competition in school or uni, or something entirely different.
Thoughts anyone ^^?