To me the filly just looks like a buckskin. But in her darker baby photos to me she looks like a sooty dun.
Also I once had a buckskin filly whose mother was a flaxen chestnut, and the sire was a black tobiano. The genes in some are passed down through generations and don't always show up on every descendant. Another example, sort of, is we had a sorrel gelding, I don't know what his sire looked like, but his mom was an average chestnut QH. His grandsire was Zippo Pine Bar, and he came out looking exactly like him. I mean, everywhere we went he turned heads, and every class we were in he got a ribbon.