Having trouble with this filly

[Eugene]

https://www.horseworldonline.net/horse/profile/2704688

Any idea what this filly could be? I was thinking Sable Cream (Brown Cream Champagne), but I can't find any browns in her recent lineage unless her dam isn't Classic Champagne.

[BlackOak2]

https://www.horseworldonline.net/horse/profile/2704688

Any idea what this filly could be? I was thinking Sable Cream (Brown Cream Champagne), but I can't find any browns in her recent lineage unless her dam isn't Classic Champagne.

Not a sable cream, though I can see why you might say that.
This is a Classic Cream Grulla, or at least, that is my belief. No stripings like the sire, but that does explain her light coloration.

Brown hides underneath bay, so technically speaking, the brown gene could've remained entirely hidden all the way from the original AC breed. That's a long shot, it should've popped up somewhere along the line, but it can. However, that's not what happened with your horse.
For your information on your sire, the buckskin dun (aka dunskin), he has only one agouti and that is a bay. So he can only throw bay or black offspring with a black mate.