64. The homily, which is given in the course of the celebration of Holy Mass and is a part of the Liturgy itself, “should ordinarily be given by the Priest celebrant himself. He may entrust it to a concelebrating Priest or occasionally, according to circumstances, to a Deacon, but never to a layperson. In particular cases and for a just cause, the homily may even be given by a Bishop or a Priest who is present at the celebration but cannot concelebrate”.65. It should be borne in mind that any previous norm that may have admitted non-ordained faithful to give the homily during the eucharistic celebration is to be considered abrogated by the norm of canon 767 §1. This practice is reprobated, so that it cannot be permitted to attain the force of custom.
66. The prohibition of the admission of laypersons to preach within the Mass applies also to seminarians, students of theological disciplines, and those who have assumed the function of those known as “pastoral assistants”; nor is there to be any exception for any other kind of layperson, or group, or community, or association.
Nuns like most monks, brothers and, obviously, laypeople are not ordained. Only priests are ordained.
If a nun truly gave the homily, the priest allowing it erred.
None of you peons are allowed to read the Bible. Ever. Only the Catholic High Priests are allowed to read and interpret the Bible. They will tell you what it says.