Fantastic film and borderline masterpiece imho.
***SPOILERS BELOW***
All the women at the end was basically Lars von Trier showing that her situation wasn't an isolated case and that all women are evil!!!
When she was in the cabin the previous year she convinced herself through reading/research that women were evil, beleiving she was evil was what motivated her choices at the end!
It's not a simple couple who are devastated by the death of their child. The child himself is Lucifer, who fell from the sky provoking pain, sorrow and desperation (the three small figures).
From then on,
sex will be only pain and punishment, Eden will be the place of the ancient fears where the 'tremendum and fascinans' mystery of the nature will be revealed.
The battle between man and woman becomes THE war of sense and instinct.
In this vision, woman becomes a totemic and absolut witch and once she's burned to death everything gets clear. The movie starts with a falling and ends with a rising. Eden is full again, nature turns good again. You can't see the uphill but you can understand it's a rising toward a bigger promise."