All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
First: One of the conditions of the validity of repentance in case of transgression against the rights of people is to return the rights of people to them or seek their forgiveness. This is in addition to the general conditions of repentance. Abu Hurayrah narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever has wronged his brother with regard to his honor or anything else, let him seek his forgiveness today for that injustice before (a day when) no Deenaar or Dirham would be there (to avail him). (On that Day) If he has good deeds, they will be taken from him in proportion to his injustice, and if he has no good deeds, the evil deeds of the person he wronged will be taken off of him and the wrongdoer will be burdened with them.” [Al-Bukhari and Muslim]
Please refer to Fatwa 86527 for the conditions of repentance.
Second: The repentant must return the material rights to their rightful owners or seek their forgiveness. As for the moral rights, like those related to honor, including backbiting and the like, the preponderant view is that it is sufficient for the repentant to supplicate Allah, The Exalted, for the one he has wronged if it is feared that seeking his forgiveness would lead to a graver evil.
Third: it is true that scholars made a distinction between rape and consensual Zina (fornication/adultery). Muslim jurists held that no right is due on the male perpetrator of Zina to the woman in case of consensual Zina, unlike the case with rape. This is because the woman, in case of consensual Zina, willfully offers herself, contrary to rape, in which the woman is assaulted against her will. Ibn Al-Qayyim said: “In case of consensual Zina, the woman is not entitled to a compensation (Diyah) because she willfully offered the benefit (for which the bride's gift is given as compensation) … This is similar to giving permission to someone to impair one of her organs (the doer would not be liable for any compensation as per the Sharee‘ah).” [End of Quote] In case of consensual Zina, the woman has no rights over the male perpetrator of Zina to seek her pardon regarding them.
Fourth: it is incumbent on this girl, who is unmarried as you stated, to repent of Zina and conceal her sin. She is not required to apologize to her family or anyone else.
Fifth: a woman is not obliged to inform a suitor that she has lost her virginity unless he stipulated virginity as a condition for marriage. In this case, it is incumbent on her to inform him, but she is not obliged to specify the reason. If she lost her virginity due to committing Zina, she is not permitted to inform him of this reason. However, she may resort to Tawriyah (i.e. to say something which has more than one meaning and intend a meaning different from what the listener is likely to understand) when needed. For example, she may tell him that she has not committed Zina, whilst intending that she did not commit Zina after her repentance, and that there are many reasons for the loss of virginity, including heavy bleeding during menstruation.
Sixth: the issue of the chaste man’s marriage to a female perpetrator of Zina mentioned by Muslim jurists is related to the commission of Zina in its true sense, which entails the application of Hadd (corporal punishment prescribed by the Quran and/or Sunnah). The lesser acts, like ‘oral sex’, as you called it in the question, are not considered Zina in its true sense.
Allah knows best.