I'm thinking there has to be something wrong with her flock genetically or maybe with what she's feeding them causing deficiencies.
Every year since I started hatching I have been hatching Blue/Black/Splash Marans eggs from a local friend of mine. I know they're well cared for and I had always had wonderful hatches, then suddenly I was having issues with the hatches. Most of the chicks looked fine but some of them looked sickly and we're DWARFED, like completely dwarfed and even with assistance I wasn't able to keep them alive long enough to even make it out of the incubator. I never did solve that mystery entirely but I think I tried 3 other hatches with the same results. It was weird to say the least and very heartbreaking but it was only from that flock so I assume one of the new hens she added to her flock had some genetic issues.
Anyway, all I'm saying is don't give up but maybe try eggs from somewhere else!