The ASOIAF universe is famed for its direwolves, associated with the Starks. But are there normal, non-direwolves in this universe? I know there are hounds, but in ASOIAF, are these descended from Canis lupus, or from direwolves?
Yes normal wolves exist in Westeros. I could include a plethora of quotes but for an idea of how many times wolves are mentioned see these queries on A Search of Ice and Fire for wolf (516 results though this includes false positives like the Hour of the Wolf) and wolves (324 results). Of course not all refer to wolves but most seem to, see an example quote below.
The Rock has been a habitation for men for thousands of years. Before the coming of the First Men it seems likely that the children of the forest and giants made their homes in the great sea-carved caverns at its base. Bears, lions, wolves, and bats have also been known to make their lairs within, along with countless lesser creatures.
The World of Ice and Fire, "The Westerlands: Casterly Rock"
Of course Arya also encounters a pack of wolves later on led by quite a large one that howls back at her, this wolf is Nymeria leading a pack of normal wolves.
Too slow, she thought to herself, chewing her lip, we're going too slow, they'll catch us for certain. Once, from the crest of a ridge, she spied dark shapes crossing a stream in the valley behind them, and for half a heartbeat she feared that Roose Bolton's riders were on them, but when she looked again she realized they were only a pack of wolves. She cupped her hands around her mouth and howled down at them, "Ahooooooooo, ahooooooooo." When the largest of the wolves lifted its head and howled back, the sound made Arya shiver.
A Storm of Swords, "Arya I"
Of course any mention of wolf/wolves in the books is almost certainly a normal wolf because direwolves have not been sighted south of Wall for hundreds of years. They are the thing of legend as with most “mystical” creatures in Westeros.
"It's no freak," Jon said calmly. "That's a direwolf. They grow larger than the other kind."
Theon Greyjoy said, "There's not been a direwolf sighted south of the Wall in two hundred years."
"I see one now," Jon replied.
A Game of Thrones, "Bran I"