I'm not really up on breeding, so can't comment on that, but would guess that rather than going 'blue roan' she is going grey. She looks very like my Ben who is solid black but was very grey on his face, ears, and legs by the time he was 5. I was surprised at how early it started but I quite like the look.
Harry in contrast also black has hardly a grey hair on him at 6.
I was told it was because I had clipped him quite short from a young age, don't know if that is true or not. Angel looks gorgous a very pretty girl