Yes, it would have been much less confusing if there had been foreshadowing. In the film, she is hysterical and nearly insane when Lars Hanson finds her in the house because she is so terrified of the wind and sand. She is so afraid, she may not have a grip on reality as it is very possible she imagined the whole meeting and killing which explains why there was no body visible outside. Yet she goes from hiding from the wind and hallucinating dead bodies to suddenly loving it only a few minutes later.
Yes-- a miracle recovery and transformation. It's rather unfortunate the film-makers had to compromise the artistic integrity of the story for such a tidy, wholly unbelievable ending.