X2, great advice Silkie.
I add juveniles and reintroduce quarantine chooks by putting them in a cage inside my main run for 2 or 3 days, then pop them on a roost at night when reintroducing. You've got quite a bit of space at your place, was she not able to get away somehow? The problems I've had with bullying always seem to be in the runs, not out free ranging.
Tip on force feeding. Had to do it last spring with some chicks. Found that using a wooden scewer (pointy end, you know the kind you make shish-ka-bobs with) to pry the beak open was gentler and more effective than my fingers squeezing them.