My mother hen has gone through two spells of the very same squatting and walking backward/ head twitching behavior! She did it the most during the times she was approaching broodiness and throughout the incubation time. It was difficult to treat during this time as well, as she ate very minimally and I had to pick her up off her eggs (which she hated) to allow her to stretch her legs and get food and water. Sometimes she’d avoid the snack and run straight back to her nest! Luckily she recovered both times (2 batches of chicks), but it wasn’t until she started pickup up the calorie content of her meals again. Good tip about the canned tuna, I will try that if needed again. Also I recommend Rooster Booster vitamins and electrolyte powder. I do a little sprinkle on their food each day (more efficient than placing in their water, due to frequent water changes). Good luck!!