Broody hen wil sit tight on the nest, I have a singular hen displaying the same symptoms but this was due to loss of a friend, she has never layed since. You could build an isolation coop, a old rabbit hutch will suffice check her feces, disgusting but it will give you clues on whether she is...
For aggression, I recommend purchasing a rooster (if it is no inconvenience) as it is like to stop squabbling concerning the pecking order among females. I had a female who, consequently was traumatised and despite her continuos effort never layed and egg, there be some discomfort. With my own...
My new chicks where settling in, until I (it seems) accidentally traumatised them by accidentally tripping over their coop, I have been putting so much effort into looking after them, but now I don't know what to do.