I missed seeing your thread last night. Dorothy definitely has a problem that needs treating. When a shell-less egg appears intact, it's not a crisis, but calcium citrate needs to be administered until the hen is laying normal eggs again. If a thin-shelled egg is discovered collapsed in the nest box, same thing, not a crisis, but she needs calcium therapy.
It's when you have evidence of an egg collapsing inside that I feel an antibiotic is necessary to head off possible infection caused by the yolk and the irritation of the tract. Once infection takes hold in the reproductive tract, it then becomes a life threatening situation, and if the hen doesn't die, as you realize, it can mean a case of EYP slowly killing her.
I treat this with amoxicillin. I suggest you use it for Dorothy and give her the full ten day treatment.
I've been feeding all flock feed for ten years and have had only two instances where eggs have collapsed inside the hen. I can't say I've seen any problem with my eggs being of poor quality because of not feeding layer. Of course, as my hens are laying regularly into their sixth, seventh, and sometimes eighth year, occasionally, an egg will be a little thin-shelled. I had this problem with Lilith, my eleven-year old SLW two years ago when she was nine and still trying to lay. She was the only one of two that I ever had to treat with an antibiotic due to an egg collapsing inside her. It was her final egg, but she's still spry and leading a normal life for an ancient hen.
