Are therapists allowed to refuse to help certain people?

If a therapist has a bad or problematic history with a certain person… and if later in life that person chose to seek therapy… ironically the same clinic or office that, that particular therapist worked at…

And if that person for whatever reason asked for that specific therapist, despite knowing the history they had with that person.. (or if the people at the front desk thought they’d be a good fit depending on what that person was seeking therapy for)… I believe when therapists get new clients… They’re likely either emailed about it or they have to file certain paperwork with it revealing their name… I know they’re notified somehow about getting a new client and their first and last name… say the therapist saw the name that was on file… Recognized it… Remembered the bad history with that person….

Would that therapist be allowed to tell their boss “no I’m not working with that person, I can’t stand that person. We have a bad history”… would they just reach out to that client and say that they had to get a different therapist… or would the original therapist that client chose have to work with them regardless?