|To paraphrase Gertrude Stein, a friend is a friend is a friend. Friendship is not switched on in one situation and off in another. If your friend feels that your work environment calls for more decorum or distance, that is something that both of you should have already discussed and understood.|
However, before moving this friend into the acquaintance category, you should tell her about your perceptions of her behavior at work, and then listen. Perhaps she is extremely busy or has been told by her manager that she socializes too much. Or, maybe she believes that showing friendship on the job is a sign of unprofessional behavior. While she still should have let you know about such matters, that could explain her behavior. There could be any number of other explanations as well.
The best step is for you to discuss your feelings with her. If you are truly friends, you should be able to reach a solution that maintains and even strengthens the friendship. However, if this discussion goes nowhere, then you know exactly where your friendship is going as well.