What is the practical definition of zina and in what category does any of the close to zina related action fall under? Are there any rights to be restored? Is a woman islamically still a virgin if her hymen got broken with a finger of a non-mahram man or engage in oral sex? Can she still marry a chaste man if her repentence is not good enough?

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.

There is the actual Zina (unlawful sexual intercourse), of which the Quran spoke, describing it with the most hideous descriptions, as an act of immorality and an evil way, and stated the obligation of executing the Hadd (corporal punishment) prescribed for it. Scholars defined it as follows: “The penetration of the head of the male organ into a woman’s vagina without marriage.” And there are acts that are described as Zina because they lead to it, but they are not actual Zina. These include what was mentioned in the Hadeeth narrated on the authority of Abu Hurayrah where the Prophet said: “Allah has decreed for every son of Aadam his share of Zina which he will inevitably commit. The Zina of the eyes is (unlawful) looking, the Zina of the ears is (unlawful) listening, the Zina of the tongue is (unlawful) speech, the Zina of the hand is (unlawful) gripping, the Zina of the leg is walking (to places where a person intends to commit immorality), the heart yearns and desires, and the (person through his) private parts may or may not put that (desire) to effect.” [Al-Bukhari and Muslim]

This includes inserting a finger into the vagina, and what you called “oral sex”. A woman who lost her virginity without engaging in full sexual intercourse is not considered a non-virgin. Rather, the Sharee‘ah rulings applicable to virgins apply to her, like seeking her permission (in marriage) and the like. It is mentioned in Al-Mawsoo‘ah Al-Fiqhiyyah that: “A woman who loses her virginity without sexual intercourse because of a violent jump, or (insertion of) a finger (into the vagina), or heavy bleeding during menstruation and the like, is considered a virgin in actuality and in terms of the Sharee‘ah ruling. The loss of virginity due to such reasons and their like has no effect on forcing her (into marriage without her permission) or on seeking her permission and consent …” [End of Quote]

The female perpetrator of Zina, who, according to some scholars, is required to repent to be able to marry a chaste man, is the one who committed actual Zina. As for the female who committed lesser acts, their view does not apply to her and there is nothing wrong in her marriage to a chaste man.

The female who willingly committed Zina has no right over the man with whom she committed Zina. As for the one who was forced into committing Zina, it is incumbent on the man who forced her into it to pay her a dowry equivalent to the dowry given to a woman in her standing. Some scholars are of the opinion that she is entitled to an equivalent dowry plus compensation for breaking the hymen. The same applies to a woman who lost her virginity by insertion of a finger, as the man is required to pay her compensation for the offence of breaking her hymen if he did so without her consent.

Allah knows best.