So I set forth creating a polymer-clay skeleton - and after about a month of trying to do free-floating ribs, I gave up and did a solid ribcage as you'll see here. I also struggled with making mistakes in my initial skeleton (the spine didn't arc forward enough, the spinus processes (processi?) were far too exaggerated, fat 'cankle' bases to her tibias) and since polymer clay is a far less forgiving medium I had to compromise a few times in order to finish in reasonable time. I did hack in and shave down the cankles to a less egregious state (still a bit fat, perhaps) but the lower leg muscles and ankle details are sadly mushy due to this late-game fix.
She also ended up more muscular than your average female - even than the average 'athletic' female - this one is a body-builder \ long-distance uphill cyclist. But I'm alright with that, it will be useful for future reference to see more exaggerated muscles.
As an aside, this is the first sculpture I have cured using my brand new labcorp oven - it's a forced-air convection oven that is PERFECT for polymer clay. It bakes at a perfectly even temperature throughout, and even tiny extremities don't burn or even discolor after extended baking. It's perfect. Did I mention it's perfection? After years of dealing with damaged or ruined sculptures cured in conventional kitchen ovens, I am thrilled to know that from now on I have something that won't wreck hours and hours of painstaking work.