To the Lightning by Catherine Ennis

Chris is a lonely lesbian on a longed-for camping trip with that one special woman. The problem is, she does not know whether Merry returns any feelings beyond simple friendship.

Then the two of them are caught in a lightning storm of such ferocity that Chris loses consciousness, to awaken in a forested, uninhabited valley far removed from anything she or Merry have ever known before.

They soon realize that they're stranded - cut off from civilization and rescue. Their survival in this primitive world will depend on the few supplies they've taken with them, along with whatever they can salvage from their storm-wrecked VW station wagon - and what they can devise with their own integrity.