You have to figure out what she is discounting it from first. If she considers 33% to be "full water" then you would add 20% to the total concentration. (Even though it's a "discount" a higher % solution = less water). I would do the math for example: 33% solution full water + 6.6 (I got this number 33x.2) = 39.6% or 40% lye concentration.
I don't know if that's correct or not - I don't understand the phrase "water discounting", so I have never pursued this line of thinking. In my world, you need equal amount water and lye to make soap. Anything after that is adding water, therefore you cannot discount water and make safe soap. Lye concentration or water to lye ratio should be the only terms we use. A good soaper would tell straight up what lye ratio or concentration to use instead of saying "discount" and not telling you what the starting point is... because really it could be anything. I typically soap at 25-28% concentration (although I'm experimenting more with 30-33% concentration lately), but my friend soaps at 37% concentration, so a 20% discount would be very different between our two recipes based on the starting point. [Stepping off my soap box now.]
Back to point... I would look at Katie's regular recipe to see what her lye concentration is and do the math from there. It's been many years since I bought my piping set and I wasn't impressed with her recipe, so the details are no longer in my memory as how she presented the recipe. I know it's exclusive and can't be shared here.