Edna - maybe people wish to 'diagnose' because the thought that someone has a disorder is easier to deal with than the thought of someone being pure evil.
I've pored over the criteria and ExNDN certainly ticks all the boxes.
Her MO is this. Become your friend. Draw you out. Worm her way in, convince you she's your best friend, take over your life, go after your husband, then when you find out and take objection, she'll stalk and harrass you, bully you because A) you object to this behaviour and, of course B) it's all your fault anyway. She'll bombard you with texts, letters, go in your garden and pull plants up etc, make your life hell because you don't want to be her friend anymore, display terrifying behaviour in YOUR home (that the police tell you warranted a 999 call) cackle through the walls until fuck'o'clock, try to turn people against you, shadow your every move, and get her husband (who is fully aware of what she's done, to you and others) to have a go at you outside the school because you were apparently giving her dirty looks (I wasn't and I always wear shades out anyway so how would anyone know); I told him some home truths.
The ONLY reason I forgave DarlingHusband was because I discovered we were simply the latest in a long line. It's what she does, it's what she's doing right now.
The annoying thing is that the previous Christmas I had a niggling feeling that she wasn't as sweetness and light as she made out. Stories that didn't add up, the long line of ex-best-friends, things like that. But I dismissed my subconscious thought. Of course, I would go through it all again because ultimately, repairing the marriage led to the birth of my monderful son. However, if I had my time again, I would have dialled 999 on 'the night of the demon', and I would have bitchslapped her before hopping into the removal van. (I think she instinctively knows how to choose victims who won't retaliate though 
)