I am glad you found a good therapist and made so much progress. What was unclear in your story for me was its beginning. Ointment for pinworms? Medications to treat pinworms are usually taken by mouth. See, e.g., Mebendazole - Wikipedia

Also, evidence of pinworms is more typically found in the toilet or on underwear, and yet your mother did not try to examine your worn undies, nor did she ask you to show her how you went to the bathroom before flushing.

Either your mother was misinformed or she had a hidden agenda when she asked you to spread your buttocks.

I am fairly familiar with the subject of intestinal parasites both because it both frightened and fascinated me in middle school in our biology class and because my grandmother's sister, a scholar, wrote her dissertation on the most prevalent parasite in her geographical area, and the dissertation was a significant contribution to public health and epidemiology in her day and age. It has been decades, though, and I checked online just now to make sure that what I remembered from middle school about pinworms is actually true. It is - the treatment is systemic and the evidence is not found by looking at the **** opening of a child. And if you think about it, it makes total sense that the medication would be systemic and not topical because pinworms live parasitically inside the intestines, so the medication needs to reach inside the body and topical ointment lacks that power.

I am very happy for you to have found a wonderful therapist, but at the same time a little surprised that she did not question your mother's motivation, because it should be obvious that ointment doesn't treat systemic infestation with intestinal parasites.