Will A Really Really Big Brownish/Black Spider Kill My Dog?

The other night my dog, half whipit half rat-terrier, had a GIANT dark brown hairy spider on her back, it didn't move until my friend tried to get it off of her, unfortunately we had to kill it, but we were not sure if it was poisonous or not. I am thinking it was a wolf spider, and so far they seem harmless...to humans. I am wondering if she got bit, will it kill her or make her sick?