Mare has a strong, clearly defined dorsal stripe, distinct shoulder barring, face shadowing, and leg barring.
This friend's mare is bright red bay but shows very distinct dun factor markings. But as far as I'm aware, cannot possibly be true dun.
All that being said, I'm feeling sooty red dun from your mare. The pale barrel is exactly the same shade as a friend's red dun QH gelding, and sooty can darken a horse significantly.