Not knowing the status of black in stallion and mare, as well as not knowing what the agouti and roan status is of the mare, here are your possibilities if the stallion is Ee aa and your mare is Ea Aa Rr
Offspring Color Probability
She has an intersting coat pattern, is she Appy ? Or a cross? Or is she quarter? Because in the quarter lineage there was a stud horse called Old App.
My black mare with a blaze 3 white socks threw a black filly with blaze and four white socks and sire was a blue roan appy x draft.
Without knowing what colour the roans were (roan isn't a colour in itself, it's a white pattern) there is no way to accurately juudge what genes she does and doesn't have. Having produced a chestnut means she is not homozygous for black, which still fits with SunnyDraco's colour combinations.
Bay roan is a bay horse with the roan gene. Brown roan is a brown horse with the roan gene. Essentially the difference is the same with roan on top - see how the OP's horse has the paler muzzle and flank that a brown has? Another interesting thing is that a dark brown (one that is almost entirely black aside from its soft parts) looks more like a black roan than a bay roan. Note how the OP's horse looks "blue" rather than "red"?