If the listing agent is showing the premises and not allowing other agents to show it (nor allowing you to have your own representation), the listing agent is in violation of MLS Rules and certainly not conducting herself in a legal or morally acceptable manner.
As a Realtor, I would file a complaint with the Multiple Listing Service and local board of Realtors against this person. She is obviously only interested in getting the deal for herself and is certainly NOT working in the best interest of her client.
I would also let the stratus agent know what you encountered. He should be informed of the improper behavior of the listing agent.
This kind of behavior is appalling!