They took it away with the new format and I miss it for cheering people on. I will keep trying.
Wow, I have 4 broody's to! Since you haven't seen any signs of illness, I would say age.. even though she doesn't seem that old to me. The feather fixer (18%) is essentially 2% more protein than layer (16%). Feather fixer also used to contain sulpher in order to combat mites that cause feather damage but no longer does. That shouldn't do it w/o effecting others as well. Feathers are made of 90% protein, or rather the amino acids therein. But sometimes things only effect the weaker ones, even they aren't visibly weakened, Chickens are prey animals and as such will hide anything that ails them as long as they can. And even if the same breed and batch, doesn't mean same parents, so genetics can play a role. Some are just better or worse than others. And hatcheries (contracted farms) may not keep their adult birds long enough to know their actual longevity. I will also say that sometimes hiccups just happen, especially if just coming into or exiting lay for the season as the reproductive system works its' kinks out.
I found another link that might be usefull. Again, I don't jump straight to disease.
http://www.thepoultrysite.com/articles/979/maintaining-egg-shell-quality/
As far as FF goes, chickens are creatures of habit and will resist ANY change. Usually it has to be introduced a couple times depending on how big and adventurous your flock is. Larger flocks do things faster. I feed only FF so there is no chance of forgetting. I feed out in the morning when I let them out and put up anything left when I lock them up, making sure they have enough 4 all day. And the wasteful beaking has all but come to an end. Keeping the feeders at the same height as their back also helps. Once you get into the groove it's easy. But certainly, you have to do what will work for YOUR lifestyle, or it ain't workin'!

I use 20% flock raiser also made by purina, it's low in calcium for the chicks only 1% but higher in protein (though still not 22%) and it's so much easier than feeding them separately which is impossible with my broody's. I provide the OS on the side. And some people feed unmedicated chick starter when they have mixed age flocks. The hens really seem to LIKE the feeds with more protein, who can blame them!
If you don't have time for FF you might consider garlic or raw unfilter apple cidar vinegar in their water to boost probiotics. It's a good thing that your flock want to eat the balanced, formulated diet! Please do your own research before adding those suggestion as I'm not truly faimiliar with them, but many people swear by it.
Now, I gotta run set up a brooder since I had 8 or more chicks hatch from new girls I wasn't sure were even fertile! Yay for my breeding program extra bloodlines).
