Confessions and confidentiality....a counsellors dilemma

Paul is a 25 year old man who has been receiving dialysis three times a week for the past 5 years, following a severe rugby injury. He has been with his partner, Rose, for the last 3 years and they have a 2 year old daughter. Recently it has been discovered that Rose is an ideal match as a kidney donor, and so they have both been going through the work-up required to get ready for a transplant. The work-up involves many medical tests including blood tests, ECG, chest X ray and kidney function tests. Also the donor is required to see a psychiatrist or psychologist who will conduct a psychosocial assessment. All is going well and the transplant operation is imminent.
Rose spends a lot of time at the dialysis unit, waiting for Paul, and she has become very friendly with one of the nurses, Sarah. Rose has just confided in Sarah that, once the transplant is over, she is going to leave Paul, because she feels the relationship has run its course. Sarah is shocked, and suggests that Rose needs to speak with the psychiatrist, but Rose pleads to Sarah to keep her confidence and not tell anyone because she is scared that they will try to stop the transplant. Sarah is worried that Rose feels pressure to continue the transplant process, and is just going through with it out of guilt. She comes to you, a counselor working at the unit, to seek advice.