@BryWisteria this was a fun read! I have thought about making a natural shampoo using castile soap, coconut milk (?) and oils. I use stinging nettle internally as a kidney tonic support - I’ve never had the tea, but if it smells anything like the tincture, I don’t think I could drink it.
While I was looking for recipes, the majority of them called for something I couldn’t even pronounce, then there was Xantham gum, and a few mentioned glycerine, arrowroot or cornstarch. I like arrowroot in a dry shampoo mix for freshening to skip a hair wash. Curious to see what you end up with.
As for the Castile soap - in my complete inexperience, I used it on my hair straight a number of years ago…of course the result was hideous! 
