Council of Trent: Session XXV, Regulars and Nuns, Chapter VII

CHAPTER VII. In what way, and what manner of, persons are to be chosen as Abbesses, or Superioresses by whatsoever other name; no one shall be appointed over two Nunneries.

No one shall be elected as abbess, or prioress,--or by whatsoever other name she who is appointed and placed over the rest, may be called,--who is less than forty years of age, and who has not passed eight of those years in a praiseworthy manner, after having made her profession. But should no one be found in the same convent with these qualifications, one may be elected out of another convent of the same order. But if the superior who presides over the election shall deem even this an inconvenience; with the consent of the bishop, or other superior, there may be one chosen from amongst those, in the same convent, who are beyond their thirtieth year, and who have, since their profession, passed at least five of those years in an upright manner. But no individual shall be set over two convents; and if any one is, in any way, in possession of two or more, she shall, retaining one, be compelled to resign the rest, within six months: but after that period, if she have not resigned, they shall be all ipso jure vacant. And he who presides at the election, whether it be the bishop, or other superior, shall not enter the enclosure of the monastery, but shall listen to, or receive the votes of each, at the little window in the gates. In other particulars, the constitution of each order, or convent, shall be observed.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).