Iranian director working in Scandinavia
Unless I am entirely mistaken director Abbasi is essentially accusing his economically privileged, Scandinavian eco yuppies of reaping the demonic result of their willingness to sacrifice the life of a East European surrogate mother in order to obtain the child they so desperately long for. Notice Louise's refusal to summon Elena's family when the girl is so obviously in distress because of fear that she might lose her emotional and economic investment. That's pretty cold.
Abbasi could be suggesting that the seemingly benign couple are engaging in some form of human trafficking based on their socioeconomic status and that the exploitation of vulnerable migrants is the real horror at the heart of the story.
The movie consistently refuses to clarify whether we're watching a codependent psychological breakdown involving both women or some supernatural phenomenon but as far as I'm concerned that only adds to its creepy allure.
Louise clearly suffers from some postnatal depression or even possibly psychosis after her recent miscarriage and her relentless focus on compensating for the loss of her daughter is plenty terrifying in its own right. I'd interpret Kasper's growing unease as guilt caused by his part in the neglect and exploitation of Elena.
Ali Abbasi's Iranian background might throw some light on what appears to be a none too subtle indictment of economically empowered Scandinavian women who feel entitled to everything including motherhood. For all her maternal urges Louise is a bit of a monster as evidenced by her angry and disgusted shove of Elena upon discovering her bleeding to death after having attempted that late term abortion on herself with the knitting needle. Not the most charitable or empathetic reaction under the circumstances.
Ultimately the child is just a child and I would suggest that Leo, the healer, is frightened away by Louise's escalating madness more than anything else.
Shelley is obviously open to interpretation as all worthwhile art. I was intrigued by it though.