Molting tends to be light in chickens under 18 months. Maybe they just haven't hit their first hard molt yet? It kinda differs from bird to bird.
Are the bare areas a problem for the bird, or do you just not like the appearance?
If you can't even get to the feather shaft with tweezers to pluck them out, I can't think of anything to do. You may just have to wait until she molts.