Lost/damaged feathers will not regrow until she molts naturally, adult chickens will molt and grow new feathers once a year generally in the fall. Keeping her locked up to regrow feathers makes no sense unless the other birds are picking on her. Being caged and separated from the flock is stressful for them, I could not imagine keeping one of my hens in a cage for more than a few days.
Depending on where you live, she could be going through her natural molt. They will look fine one day and then POOF they're half naked the next with feathers all over the place. Extra protein will help her get through the molt faster, they need it to grow new feathers so be sure to switch to something like a chick starter or all flock 20%. She will be miserable until the new feathers are at least half grown in, they tend to keep to themselves and huddle away in a corner. Mine seem to prefer staying in or under the coop more often when molting.
