@canadaguyadvise,
Well, as far as I can tell, this can have a number of reasons. Here's a few:
1) What I think is most likely is that she started a relationship with someone who is quite jealous by nature, and she has no wish to fight over your conversations with him.
2) Whereas you might have been thinking in terms of a platonic friendship, she might have been interested in more, and now broke it off since she feels it won't happen.
3) You said something that ticked her off(or perhaps you did something in the workplace that ticked her off, hard to tell of course) and now she's pissed at you.
Since it's hard to get to the core of the problem if the other party is unwilling to communicate with you, I reckon the best thing to do is to just leave it be for now. Ignore her as well, and try and find/make some other friends.
Also, has something changed in your life? Are you, for instance, involved in a new relationship?