Complex sentence: She often considers returning home, but is dissuaded by painful headaches induced by Nightmare whenever she tries to recall memories of her sisters Edith and Lorina or whether she considers if she has seen Peter before or not.
Split into simpler sentences: She often considers returning home, but is dissuaded by painful memories of her sisters Edith and Lorina that are induced by Nightmare. Alice gets painful headaches whenever she remembers her sister and whether she considers if she has seen Peter before or not.