Amy & Warren: We know Willow & Xander were friends with both Jonathan and Amy, before Scoobies. So, Amy and Jonathan probably knew each other, and all being magic users, could freely discuss the black arts. So, Jonathan introducing them at some point during season seven. I mean, they were all EVIILLLLLLL, not evil. Besides, Amy has a different definition of evil than most of us, like, occasionally saying bitch vs. Having your soul ripped out of your body.
And this is the problem with Amy in seasons 6 & 7. She is insane.
1. Freaky Friday is like the darkest magical spell you can use. Amy has to live in constant fear that it can happen to her at any time, like just walking down a street, an elderly man in a wheelchair just has to touch her while reciting a spell, and it's trapped in a dying body while "you" smiles and walks away. She may even have memories of what her mom did in her body, and may even have her mom's memories. Who knows? There's an old Star Trek Theory that the Transporter kills you, then simply creates a copy with no meaningful continuity between the two entities. Maybe that's how body switches work to a degree?
2. Amy lives in constant fear of becoming a Rat again. Or, or another Magic user turning her into a rat again. I doubt she's what someone else calls a "Animagus," so it was forcibly being turned into a rat. I'm sure she never lost her taste for cheese.
And who is the one person, who can turn her into a Rat, or rip her soul out of her body? Willow. So, Amy's goal is to make sure that can never happen to her again, even if Willow is her friend. So, massive trust issues, paranoia, mind warped by the dark arts. She's crazy, but in a completely sympathetic way.
Which goes back to Warren, Amy hates her mother, and probably despises her father as weak. She is also afraid of her coming back. Having a few magic users, one who wouldn't be opposed to building an army of anti-fembots wouldn't be a bad idea.