If your co worker tried to ghost you after the first date, she most likely didn’t enjoy it or a particular part of it.
If you noticed that the date ended weird, you must have sensed that something went wrong.
Even though you don’t believe that you did anything wrong at the date, she must have felt differently.
In taking her behavior to the point where she is now giving you the cold shoulder, there may have been something that you said or did on that first date that really turned her off.
It is best to give her space at this time and try not to put yourself in one-on-one situations with her at work.
This would only make her feel that much more uncomfortable.
If you keep your distance, her behavior may become more friendly with time.