My son’s aba therapist made us a social story. He was doing exactly what your daughter is doing. We had to have him in a backward sleeper, taped up so he couldn’t reach to open. It was such a difficult time. I really feel for you.
I read to him the social story while seating him on the toilet. We did designate a specific candy for a successful poo in the toilet. I’m not above candy. But once he did it’, that was it, thankfully. Wishing you good luck.

It’s sensory thing I think and there are sensory activities YouTube that will give you ideas but using this she might not feel need to smear. It’s replacement activity and so stimulated by play. Do keep trying to train her and involve professional like behaviour therapist or occupational therapist