You said the bird worried you from the get go..
That looks very similiar to birds who had a high load of parasites/malnutrition/strong illness in the beginning of feather growth and the lower growth of the feather was well feed/nourished and grew in normally.
Basically when the bird is sick, there is less energy going to feather growth and you can see the healing process coming out in the feather. When the bird gets better, the feather growth will start to look better also.
The lower part of the feathers looks well formed, so whatever ailed the bird that caused the feathers to start a weak growth, has been gone.
I have more experience with wild birds, but I have seen enough similiar feather damage with them. And much more extensive damage where the wing feathers were like feather-dusters(no connection so its structure turned out like silky feathers) or had horizontal stripes and broke off there.
The feather is basically showing you the history of her life.
A rough start, but it went better and is now gone.
It will molt normally whenever the chicken is due with it, and the new grown feathers will look normal.
Whatever caused the rough start, the feathers show that you managed to make it go away.