Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XXV

p. 75 Canon XXV.

One who had betrothed a maiden, corrupted her sister, so that she conceived.  After that he married his betrothed, but she who had been corrupted hanged herself.  The parties to this affair were ordered to be received among the co-standers after ten years [of penance] according to the prescribed degrees.

Notes.

Ancient Epitome to Canon XXV.

A certain body after being engaged to marry a young girl, violates her sister and then takes her to wife.  The first is suffocated.  All who were cognizant of the affair are to be subject to penance for ten years.

I have followed the usual translation “hanged herself,” which is the ordinary dictionary-meaning of ἀπάγχω, but Hefele says that it signifies any and every variety of suicides.

Balsamon.

In this case we have many nefarious crimes committed, fornication, unlawful marriage [i.e. with the sister of one’s mistress] and murder.  In that case [mentioned by St. Basil in Canon lxxviij. where only seven years penance is enjoined] there is only a nefarious marriage [i.e. with a wife’s sister].