Where was she tested for agouti?
Other than that, she is homozygous red and heterozygous for cream.
Honestly, your best bet would probably be a dunkskin stallion, like SBR Formula One website
if you want the possibility of getting all of those colors.
ETA: After rechecking, he's homozygous black, so your possibilities would be buckskin, dunskin, perlino, perlino dun, bay dun, and bay.