sheep leather was exactly what she used.
I thought about sanding the under side of the leather, but that may make it even more fragile than the original from medicom and get uneven thickness all over... also, there is the line with which you sew... have to be a much thinner one. We'll see if we can improve the model with what we got here and maybe she'll even put some on ebay. I'll let you guys know if that happens.
The one from facebook seams to be a paper thin synthetic imitation of leather. It's hard to understand how some parts could have been done, as there is fabric over fabric without adding much thickness.
how much fabric is there in the jacket? i can't really see the details from the photos. but if there are fabrics, you may just want to use them on the collar area where it is actually exposed, the rest could skimp on the fabrics and will make it less bulky.
for thinning the leather, i think it's been done before. you just need a sanding block to get it more even. The top layer is relatively strong.