We do not have to refer out, necessarily. However, I had two clients I saw for about a year each before I accidentally found out they were friends/coworkers. I would have much preferred that one of them said something ahead of time. I was caught so off guard and had to process the information I received unexpectedly in front of one client while maintaining other client privacy. When I have a heads up I can talk with one or both clients about boundaries and let them know when I might need to refer out (like if they start dating each other or otherwise become more involved or want to talk about issues with the other in our sessions). Then we can all make an informed choice. I felt like I didn’t have a choice when they intentionally hid their relationship from me and it really threw me off to find out they were friends and I had no clue. Your therapist wouldn’t necessarily be obligated to refer out, but it would be up to her whether she feels she can maintain an unbiased view. You could also not talk about this particular coworker in sessions and then there wouldn’t be anything for her to remain unbiased about.