I think it's definitely possible to feel deeply connected on a spiritual or soul level. Therapy works best when there's a good fit (chemistry) between therapist and client but pursuing a romantic relationship is a big no no, because the odds are it won't work out and could be extremely damaging. I would imagine the same goes for friendship too, at least while you're in therapy together. If there's a good soul to soul connection, bingo! you've struck gold, Keep them as your therapist

She has the definition of twin flame all wrong. Twin flames spend most of their life times pursuing or running away from each other. Also, you can't rule out transference and counter transference, because it's always there on some level (like it is in most relationships).