Look, while some of the stuff is uncalled for like calling you bitchy, it is possible she just acts like that generally. Some people just act in a kind of flirtatious manner with the friends, because that's their personality. Therefore they don't realise that what they are doing is viewed as actual flirting to the other person, as they do it to all of their close friends. Therefore when the coworkers call you love birds and so on, they consider it to be a joke, because to them, you are nothing more than close friends at work.
That being said, the way she has acted after you asked her out has been pretty inappropriate. While it may well be motivated by a sense of awkward confusion from discovering you had feelings for her, it doesn't justify persecuting you for putting yourself out there. If she's actually a good person, she'll see what she's doing is wrong and stop mocking you, and if she doesn't then that suggests that she lacks compassion and you probably shouldn't be going out with her anyway.