Ok I'm no expert but I'd say if dorsal stripe then dun, but if that disappears then bay, I'd expect her to go lighter as she gets older until she sheds her foal coat.
My yearling is a very unusual Fox Dun - he looks like a bright bay as he has a black mane & tail, but he has the dorsal stripe and his mane and tail actually have light coloured streaks through it. Also his 'black points' on his legs are actually chocolate, not black as you would find in a bay! His mum is chestnut and Dad is dark bay.
and is actually the foal pics above (I am new owner and just recognised him as he's quite an unusual colour, but from the photos he now looks like a bright bay!)