Responsa for Bekhorot 60:35

Q. A's wife bound herself by a ban in the presence of the people of the town, not to do a certain thing. The terms of the ban were written down, and all the townfolk signed the document. Subsequently she transgressed the ban several times, as attested to by witnesses. A transgressing woman, if properly forwarned, loses the right to her ketubah. We are doubtful, however, whether A's wife had to be properly forewarned before losing her right to the ketubah. We are inclined to believe that no such forewarning was necessary since she was warned at the time the ban was pronounced that she would lose the right to her ketubah should she transgress the ban, and she agreed thereto without inserting any qualifying conditions. Does A's wife lose the right to her ketubah? Furthermore, is A permitted to divorce her against her will?
A. Even if proper forewarning were required before a transgressing woman loses her right to the ketubah, one such warning would be sufficient. Otherwise a woman would be able, without any restraint, continually to cause her husband to sin. For, when forewarned by witnesses, she would temporarily abstain from sin, and, later, return to her mischief. Moreover, any situation that would require the administration of testing-water to a Sotah (a woman suspected of faithlessness), would cause her to lose the right to her ketubah; and the forewarning of a jealous husband, even though preceding by many days the seclusion of his wife with another man, would require the administration of testing-water, as evidenced by the statement of the Baraita (Yeb. 58b): the jealous forewarning of a betrothed would require the administration of testing-water after she married [if she secluded herself with that other man after the marriage took place]. Therefore, a forewarning does not necessarily have to precede a transgression immediately.
The question was again sent to R. Meir: A's wife brought witnesses who testified before us that A also had transgressed the ban. We decided, therefore, that she did not lose the right to her ketubah, since she did not intend to commit a sin. Moreover, a woman must be forewarned immediately before committing a sin in order to be classified as a transgressing woman. The Baraita cited above offers no proof to the contrary since it deals with a case where the sinful seclusion immediately followed the jealous forewarning (i. e. the seclusion took place before the marriage).
A. I still believe that a forewarning does not necessarily have to precede the transgression immediately. Thus Rashi offers two interpretations of the aforementioned Baraita. The first, and most important, interpretation assumes that the seclusion took place after the marriage, and, thus, long after the jealous forewarning. Moreover, the Talmud (Sotah 26a) clearly states that a woman who was jealously forewarned before her marriage and secluded herself with another man after the marriage, must either drink the testing-water or lose the right to her ketubah. However, since A too has transgressed the ban, we must make two distinctions. a) If the wife's sin consisted of merely disregarding the ban, while her act was not sinful in itself, A is not permitted to divorce her; for transgressing a ban causes the death of the transgressor's children, and is, therefore, ground for divorce; but, since A himself transgressed the ban, he can have no objection to a similar act on the part of his wife. b) If A's wife, however, transgressed Mosaic law and Jewish custom, A is permitted to divorce her even against her will; he need not seek the consent of the communities, and he is not required to pay her the ketubah.
SOURCES: Cr. 185; L. 393; Tesh. Maim. to Nashim 16; Rashba I, 864–6; Hag. Asheri Ket. 7, 9. Cf. Isserlein, Pesakim 68.