Both my children went through this phase. They didn't like water in their faces, but were even more scared of the SOUND of the shower. So I put them in the bathtub and I took a small bucket (the one they played with on the beach) and diluted some low-poo/co. in it and rinsed that through their hair. After that I rinsed with plain water from the bucket.
I found that worked better to control their fear, because you can tell them exactly what to expect, like how many buckets of water
2b (mixed with 2c/3a) med/fine- low porosity- normal elasticity, BSL