BibTeX:
@incollection{ShoghiEffendi1982,
  author = {Shoghi Effendi},
  title = {What a Gap She Has Left Behind Her!},
  booktitle = {Bahíyyih Khánum: The Greatest Holy Leaf},
  year = {1982},
  publisher = {Bahá'í World Centre},
  url = {https://www.gutenberg.org/cache/epub/19242/pg19242-images.html},
}

APA:
Shoghi Effendi. (1982). What a Gap She Has Left Behind Her!. In *Bahíyyih Khánum: The Greatest Holy Leaf*. Bahá'í World Centre.

MLA:
Shoghi Effendi. "What a Gap She Has Left Behind Her!." *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.

Chicago:
Shoghi Effendi. "What a Gap She Has Left Behind Her!." In *Bahíyyih Khánum: The Greatest Holy Leaf*, Bahá'í World Centre, 1982.