False Dawn by Chelsea Quin Yarbro. The woman is Thea and the guy she teams up with is Evan.
The motorcycle gang fits, the couple do end up in Tahoe, and the final scene in the book is:
“All right,” he said taking the hand that touched him. “Go where you want and I’ll go with you.”
She made a miserable attempt at smiling “There might not be any place to go.”
“There might not,” he agreed. There was a moment of silence between them as the wind grew sharper. Then she turned southward again, and keeping his hand tightly in hers, she led the way into the dark mountains; and the snow that followed them covered their footprints as if they had never been.
Thea uses a home made crossbow not a bow and arrow. The scene where she kills the woman is:
One of the women wasn’t dead yet. Her ravaged body hung naked from a broken billboard. Her legs were splayed wide and anchored with ropes; legs and belly were bloody, there were heavy bruises on her face and breasts, and she had been branded with a large “M” for mutant.
Thea watched stonily from the shadows, fitting a quarrel to her makeshift crossbow. Then she braced her forearm and pulled the trigger.
The high sobbing laughter was cut off with a bubble and a sigh as the quarrel bit into the woman’s neck. There was no sound then but the snarling of dogs, and tearing.