Make sure she is getting her turn at the feeder, and not being bullied away by the others. Make sure she has a full crop of food at night when she goes to roost. If she isn't getting enough food, you may want to hand feed her daily, or add another feeder. You could also try giving her a couple of drops every day, of ply-vi-sol by her beak, in case she has a deficiency. Check her droppings to make sure she doesn't have diarrhea--could be a sign of worms. And of course look carefully for mites and lice.