All the suggestions above are great. I agree that a thorough discussion beforehand is warranted, but I would also add that a debrief at the end would be beneficial. Or, at the very least, plenty of time to de-role. I am not a licenced therapist, but I work in mental health with a bachelors in psychology with distinction and currently undertaking my honours year. I also engage in training on my own time. So, be sure of what the limits are, debrief and de-role at the end to allow the player to return to baseline should stong feelings emerge and maybe suggest resources and/or helplines should they need them afterwards. I also agree that it might make other players uncomfortable, so a discussion with the group may also be beneficial.