To what extent is a committed Muslim woman's claim true that her female follower strangled her fetus in her womb, and did the recitation of one of the female shaykhs when she became pregnant again enable her to give birth safely?

Every human being has a qareen (companion) from among the jinn, as proven in the hadith of Aisha, agreed upon [by Bukhari and Muslim]. This qareen may act in a way that harms the human, but it cannot be definitively stated that every harm is due to it. To protect oneself from its evil, one must seek refuge in Allah through supplication and by regularly reciting the morning and evening adhkar (remembrances).