Re: When woman is allowed to ask divorce?
In Islam, men and women are equal (with different responsibilities and duties). Regardless, they are responsible of their deeds and would answer only for themselves on judgement day. Thus, both men and women have same right to divorce (Talaq or Khula) each other. Man can divorce (give talaq) his wife for any reason he wants to and same way woman can divorce (take khula) her husband for any reason she wants to. Anyhow, there is slight difference in procedure, due to involvement of money ('Mahr').
When man divorces (give talaq), he forfeits amount he paid as Mahr to woman, so he can divorce without going to court.
When woman divorces, she loses the right to keep Mahr, and for that reason she has to go to court, and court make sure that mahr is returned (or mutual agreement or understanding too place regarding mahr) ... or ... she can ask her husband to divorce her (that can happen without going to court).
As marriage is contract, in the contract, with mutual agreement or understanding, woman can also get right to divorce (clauses can be added in nikah-nama ... an agreements of marriage contract). Such agreement would make mahr irrelevant, as in this situation, woman can give (or take) divorce without returning mahr, hence no need for court (and judge).
In Islam, it is recommended that when divorce situation arises, people should try to mediate to discourage divorce, because divorce has implications and if divorce is due to any trivial misunderstanding than that divorce should be avoided.
Taking that recommendation into account, some people (so-called religious scholars) have started interfering with divorce (especially Khula), enacting conditions for divorce. As khula needs court and judge for procedure, this recommendation is mostly related to Khula ... but such recommendation is only recommendation, and have no place as far as Islam is concerned.
As for husband telling her wife not to visit her parents or relatives, that is against Islam. If wife listen to her husband than she would be doing sin, as she is ignoring command of Allah in Islam, that one should look after parents in every way and should try to have good working relationship with blood relatives. Thus, she would be made answerable to Allah (and obviously parents), on judgement day.
[One should remember that anything that is fard or told by Allah to do, then to forgo that due to fear of Husband, consequences, or anything in this worldly life, would be sin ... rather, big sin when it comes to ignoring parents].
Unfortunately, in country like Pakistan, due to Hindu culture, divorce is seen as taboo, and thus women get a hell of treatment, enduring everything just to keep marriage going.
This practice maybe prevalent in other Muslim (and non-Muslim) countries and culture too, but that is due to reason most religion sent by Allah got corrupted by humans, and obviously, concocted religion have done the same, made men superior to women in relationship. Even though both are equal (with different responsibilities and duties when it comes to marriage), and would get rewarded or suffer equally for their deeds after death.
Note: Islam do not consider divorce 'taboo'. Even Prophet (SAW) once wanted to divorce his wife Sauda (RA) for no particular reason. Secondly, Quran also directed Prophet (SAW) to tell his wives that whoever wants good worldly life than he (SAW) is willing to give them enough worldly goods along with divorce.
Actually, the above verse in Quran tells that wife can also take divorce whenever they like if permission by husband is granted (at any stage of marriage) or clauses is added in marriage contract (nikah-nama) with mutual understanding.
If divorce was such a 'taboo' thing in Islam, what some people like to portray, than Prophet (SAW) would not have showed his intention to divorce Sauda (RA), who was the first wife Prophet (SAW) took after the death of Khadija (RA). Similarly, Prophet (SAW) would not have approved divorce of Zaid (RA) and Zainab (RA), where there seems no reason that they should have got separated, except the reason Zainab (RA) was from well to do family, and Zaid (RA) was freed slave, something that became incomparability between them. ... Neither it would be in Quran telling Prophet (SAW) to tell all his wives that if they want divorce they can have it any time.
Quran 33:28 (Yusuf Ali):... O Prophet! Say to thy consorts: 'If it be that ye desire the life of this world, and its glitter, then come! I will provide for your enjoyment and set you free in a handsome manner.