Yeah, recessive white dilutes everything from the start, it’s an extreme example of leucism (not quite albinism). It’s really odd that the pattern would change like this though, it’s like it’s a different phenotype now. The fact that you think it’s passed on from the grandmother shows it might be recessive, is the grandmother the mother of her sire or dam (so we can see if it’s sex linked)?
How bad is parasitic white in your flock? That’s the only example I can think of when white would increase with age like this, but not usually in hens like this.
parasitic white in my experience is white close to the base and tips are black.