As you leave the Audliten tower (where Sveck is) turn right and follow the road west. When you receive the message that you have entered West Svealand start looking for large sveawolves either side of the road - Modervarg will be among them.
When I did the quest I found her in the middle of the road, near the loc given in the picture, but she was moving around so she may wander away.
She conned even to my L14 skald and was an easy kill.