We learned on daf 56 about the story of Bar Hedya interpreting the dreams of Rava and Abaye. Rava who did not pay Bar Hedya was always interpreted for the bad. Over the course of the interpretations, Rava's wife, who later we learn was the daughter of Rav Chisda dies.
Rava then pays Bar Hedya, who in turns gives positive interpretations for the dreams of Rava. Over the course of these dreams Rava becomes the Rosh Yeshiva after the death of Abaye.
The chronology seems to indicate that the daughter of Rav Chisda dies before Rava became Rosh Yeshiva.
On daf 62, we read about the bathroom habits of Rava, where the Gemara states that after Rava becomes the Rosh Yeshiva, (and requires an extra measure of protection,) the daughter of Rav Chisda would put her hand on the head of Rava to protect him from the mazikin.
Wasn't she nifteres prior to his appointment?
Thank you for taking the time to review this question.
Boca Raton, FL
Your excellent observation was noted by Tosfos on Daf 62, who answers that Rava's dream about his wife's death preceded the dream about Abaye's death, but in real life the former followed the latter.
In truth, we may wonder whether it is necessary to suggest such an answer, for a simpler solution would seem to present itself. One of our members, Rabbi Yakov Tavin, showed from Bava Basra 22a that Rava and Abaye both were Roshei Yeshiva at the same time. If so, stating that "Rava reigned (i.e., was a Rosh Yeshiva)", does not mean that Abaye was already dead. It is true that the size of his Yeshiva grew when Abaye passed away, but he was a successful Rosh Yeshiva prior to that time. Rava's wife passed away before Abaye, but the story of the bathroom took place when Rava and Abaye were both Roshei Yeshiva, before Abaye passed away! (It is not clear why Tosfos did not suggest this answer himself.)
Be well, and regards!