To change the pecking order I would remove her totally for at least three days, 5-7 would be better.
 I personally would send the others out into the tunnels than take that time to block them out and tend to Loser. Take her off the roosts and feed her. I have had hiding chickens, they all eventually come out. My bottom birds will either get up on the top of a pen where I feed them, or they also learned to sit inside a plastic water trough used to feed hay, I have fed them in there too. So maybe adding some things to sit in or platforms to sit on will give Loser some confidence.
 There's always a bottom bird who gets all the attacks, so you can't fix that, you just try to make their lives easier. They can't feed or roost near the top bird, it's just the way of the chicken.