Just wanted to add... The UiB ordbok actually does list "fort" as an adjective also, and gives the example, "små, forte bevegelser". But presumably it's uncommon as an adjective. Fveldig in fact says the same thing as Deliciae in another comment.
Raske is the plural form of rask so "raske menn". Rask is the masculine and feminine indefinite singular form. I think it is appropriate here because another way of looking at the sentence is "her dog is [a] fast [dog]".