What type of dun?

UC Davis does all horse genetic testing. It's $25 for a Cream test. I don't think you'd know if she was a bay dun or a dunskin unless you tested for Cream.

Actually, in the Fjord breed, it's a pretty obvious difference between the brown (bay) duns & the "white duns" (dunskins). This is what a white dun looks like:
Fjord Stallion for Stud - Deep Creek Farm, West Virginia
The OP's horse is not a dunskin.

Check this out

The Norwegian Fjord Horse

This horse is

Brunblakk




Brunblakk is the most common color of Norwegian Fjord Horses and is the color of about 90% of all registered horses (2005). It may be the effect of dun on light (wild-type) bay as it is unsure whether the bay and brown agouti alleles exist in the breed. The body coat is pale yellow-brownish, but the shade varies from cream yellow to light brown. Paler colored horses have white manes while darker horses have darker manes. In Norwegian the darker stripe of hair in the middle of the mane is called the "midtstol", while the darker hair in the middle of the tail is the "halefjær". In brunblakk the dorsal stripe, midtstol and halefjær are black or dark brown.