In this case Numbers 35:30; Deuteronomy 17:6, 19:15 there are two or more witnesses against a person, the accusation can't be denied here is a word-against-word case.
This thing must have been made known by her accusing him because there is no witnesses to it and regardless if she indeed consented or not, it's not lawful to have relation to a betrohed women, so it's either rape or adultery which is a death sentence for the man!
23 If a damsel that is a virgin be betrothed unto an husband, and a
man find her in the city, and lie with her; 24 then ye shall bring
them both out unto the gate of that city, and ye shall stone them with
stones that they die; the damsel, because she cried not, being in the
city; and the man, because he hath humbled his neighbour’s wife: so
thou shalt put away evil from among you. (Deuteronomy 22:23-24 AKJV)
25 But if a man find a betrothed damsel in the field, and the man
force her, and lie with her: then the man only that lay with her shall
die: 26 but unto the damsel thou shalt do nothing; there is in the
damsel no sin worthy of death: for as when a man riseth against his
neighbour, and slayeth him, even so is this matter: 27 for he found
her in the field, and the betrothed damsel cried, and there was none
to save her. (Deuteronomy 22:25-27 AKJV)
But perhaps she is lying! In a word-against-word case are both the accused and the single witness tried, it might be a situation like Joseph and Potiphar’s Wife (Genesis 39). "the judges shall make diligent inquisition: and, behold, if the witness be a false witness" she alone shall bear the punishment she meant to afflict on him by bearing false witness.
If a false witness rise up against any man to testify against him that
which is wrong; 17 then both the men, between whom the controversy is,
shall stand before the Lord, before the priests and the judges, which
shall be in those days; 18 and the judges shall make diligent
inquisition: and, behold, if the witness be a false witness, and hath
testified falsely against his brother; 19 then shall ye do unto him,
as he had thought to have done unto his brother: so shalt thou put the
evil away from among you. 20 And those which remain shall hear, and
fear, and shall henceforth commit no more any such evil among you.
(Deuteronomy 19:16-20 AKJV)