Having said that here are a few questions for you.
Did the current agent ask if you were working with another agent? That would have been the correct thing to do. If she did what was your answer?
This wasn't a house the other agent showed you?
Depending on your answers, I can see why the agent might be upset. One of the most valuable asset
a Real Estate Agent has is time.
The Realtor who is entitled to the commission is the one who is the procuring cause (i.e the one who showed you the property, etc). If you didn't have a written and signed exclusive contract with the prior Realtor, as long as they cannot be considered the procuring cause for your purchase, there's really nothing you can do. Let them go to arbitration.