She is actually the offspring of my original BCM flock that I sold off a few weeks ago. I kept 14 of those pullets for eggs, but won't breed them as BCM. That particular girl doesn't look so bad, but some of the others have way too much straw color in their hackles, some have eyes that are too light, and 4 of them have yellow feet. These were some of the awful flaws in my first flock, and that's why I decided to sell after hatching the first batch. It's too much to work with to try and get to SOP, but they do lay dark eggs, and will be perfect for OEs
Also, the yellow in shanks means there is a cross in that line that is not Marans. Once you see yellow shanks in a line, you cannot use siblings for BCM breeding that are not expressing yellow, as they can be carrying genes for it without showing outward signs themselves- and yellow skin can skip a generation. It's one of those things that can't be bred away by selection. It is best to find better stock for breeding BCM.