Yerushalmi Yevamot 10:5 ירושלמי יבמות י׳:ה׳

MISHNAH: If they told her, your husband died, and she remarried, and then they told her, he was alive but died, she must leave and the first child¹²²Any child conceived during the first husband’s lifetime. is a bastard, but the last is not a bastard.
If they told her, your husband died; she was betrothed¹²³But she never slept with the prospective second husband. and after that her husband returned, she is permitted to return to him. Even though the second [husband] gave her a bill of divorce he did not disable her from priesthood. This Rebbi Eleazar ben Matthew explained, “a woman divorced from her husband,¹²⁴Lev. 21:7, from the list of women prohibited to a priest.” and not a woman divorced from a non-husband¹²⁵Since betrothal of a married woman has no legal standing..

HALAKHAH: “If they told her, your husband died,” etc. “If they told her, your husband died; she was betrothed,” etc. Rebbi Joḥanan in the name of Rebbi Yannai: Her only problem would be aspersion on the priesthood, but the court will not tolerate aspersion¹²⁶The priests, who were very particular about purity of their lineage, might not want to accept the return of a woman for whom one might construe a violation of priestly rules. Even though the courts go along with some of the self-imposed restrictions of Cohanim, such as the prohibition of a toddler convert, this would be one they will reject..

How do you explain these¹²⁷All Mishnaiot of this chapter which deal with a wife remarried on testimony that her husband had died.? With one witness or with two witnesses? If you explain with one witness, then one witness would permit her to the levir¹²⁸As explained in Chapter 15, a single witness is accepted to free a widow to remarry. But in that case, Mishnah 5 implies that a single witness can lift the incest prohibition of the sister-in-law by permitting her to the levir. This is against our general rules that biblical prohibitions can be lifted only by two credible independent witnesses.
In the Babli, 93b, Rav Ḥisda accepts the argument that a single witness may lift the prohibition of the sister-in-law. It is accepted in the Babli that the restrictions enumerated in Mishnah 1 are intended to make sure the presumed widow checks carefully the truthfulness of a single witness.. If you explain with two witnesses, then it disagrees with Rav since Rav Naḥman bar¹²⁹Reading בר instead of בשם רבי, from the text in Halakhah 15:4. The last word תני is read with Halakhah 15:4 אתנו = אַתְּ (הִ)נּוֹ “you are him”. Jacob said in the name of Rav, if she was married by the testimony of two witnesses, even if he returns, she says to him, you are not him.

From where that no betrothal is valid for a married woman? Rebbi Immi in the name of Rebbi Yannai: “She left his house, went, and became another man’s.¹³⁰Deut. 24:2.” When she leaves his house she may be with another. And from where that no betrothal is valid for incestual relations? Rebbi Tanḥuma in the name of Rav Huna: “She left his house, went, and became another man’s.” Why does the verse say “another”? To exclude the list of incest relations¹³¹In the Babli, Qiddušin 88b, this is quoted in the name of R. Yannai; there the argument is rejected as insufficient. Perhaps for “another” one should translate “an outsider”. The Babli always subsumes adultery under incest prohibitions and does not need a separate argument..