First, have you engineered the floor correctly already? By that a waterproof membrane on a PRESLOPE substrate....then mortar bed on top of that, sloped to drain? If you have any questions about that part, check with the tile experts at www.johnbridge.com You can get great help there , if you need it. A good book is The Ceramic Tile Handbook, by the Tile Council of North America ( www.tileusa.com)
Anyway, I'm not sure I see why you need these pony walls. Why cant you just have a shower curb and glass up from there. The 10mm glass will of course be quite expensive, and will be a custom install.
Have you considered doing a curb, or pony wall, on the short side, and making it a walk in on the wide side?