its real hard to tell without tests,,, but if she aint black i'd say she's more a dark bay than brown.
The thing is, with breeding her to black studs, or even bays, buckskins... anything black based, is they *could* be throwing the black. What color is her sire and dam?
Normally a hetero black to red roan (hetero for roan and carrying no agouti) mating would create;
chestnut
red roan,
black
blue roan
hetero black to red roan (hetero roan, hetero agouti)
chestnut
red roan
bay
bay roan
black
blue roan
there is only minor changes to the color outcomes if the mare is genetically bay.