It sounds like she’s hurt from rejection and jealous of him dating someone else. Her comment, “Friends don’t treat friends like this.”, means to me she is especially angry that he is dating someone else from work right in front of her (the nerve!

). She is acting extremely immature. Her anger and desire to make their lives a living hell speaks a lot about another side to what you think is a good friend and nice person. I’d be careful if she turns on you.
I agree with Buffy, she may lose her job if she keeps on like this. She is harassing them and the boss doesn’t appreciate workplace romance drama.