Why can't my adopted sister accept she is not part of my family because she isn't related? Why can't she stop calling my parents mum and dad?

If you weren't aware that your sister was adopted, would you feel the way you do? My guess is that no, you wouldn't. It's time you did a little soul searching to understand why it bothers you so much and why you're so focused on the fact that she's adopted instead of realizing the gift you have in having a sister.

My son is 13. Earlier this year, we'd gone to visit my family as we usually do several times a year. My two sisters, myself and my son were sitting out on the back patio, just talking and catching up. I'd noticed that my son was being unusually quiet and had been looking between my two sisters and me. When one of my sisters went inside to talk to our dad, my son said “Mom…why doesn't Aunt M look like you and Aunt K? I mean, you and her look kind of alike, but not as much as you and Aunt K do.” I told him it was because his Aunt M is our stepsister, which was met with utter astonishment and a bit of indignation on his part. “What?! Why didn't you ever tell me that??!!” I explained that I probably never mentioned it because, to us, she's just our sister - we don't think of her as our stepsister. The only time that we describe her as our stepsister is if the relationship needs to be clarified as such. Other than that, M is our sister. Plain and simple.

When my son found out that his Aunt M was technically his step Aunt and not not blood related, did it change how he felt about her? Not. At. All.

I’m wondering about attachment and transference with the therapist and the idea of escape and fantasy? How much do you think your strong feelings, constant thoughts, desires to be with your therapist are a way to escape from your present life? I wonder if the transference serves another purpose than to show us our wounds and/or past experiences, but is a present coping strategy for managing what we don’t want to face (even if unconsciously) in the present—-current relationships, life circumstances, etc. Can anyone relate to this concept of escape in relation to their therapy relationship? How does this play out for you?

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Oh - the answer to the last part of your question (why she “can't stop calling them Mum and Dad”)? It's because they ARE her Mum and Dad, too.