Where did you get the cat from? Do you know anything about her history?
Does she have a safe refuge (like a separate room) away from the dog, somewhere that the dog isn't allowed to go? If not, that's the first thing you need to do - establish a safety zone for her with her food/litter/bed where she can feel completely comfortable. Doesn't matter if the dog isn't a threat to her, she doesn't know that. Once she's doing okay in that room, you can very very slowly work at reintroducing her to your dog (using lots of treats and praise and going at her pace).
You'll need plenty of patience and understanding. Some cats will never feel comfortable around dogs, so be prepared (make sure she has lots of vertical space she can escape to, and constant access to a dog-free zone). It could be that she's had bad experiences with dogs in the past, or simply that she's never been socialized to them.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler