What is the ruling of Islamic law on forcing a girl to postpone her marriage until her older sister marries, and is she entitled to resort to a judge to marry her in this case?

The Shari'ah has granted women wilayah (guardianship) in marriage to protect their dignity and interests. It is incumbent upon the wali (guardian) not to prevent his ward from marrying a suitable suitor whom she approves, under the pretext of waiting for the older sister to marry first. This goes against the Shari'ah and can cause animosity between the two sisters. This is a common custom among ordinary people that has no basis in Islamic law. Ibn Uthaymeen said: "It is not permissible for a father to prevent a suitable suitor from proposing to his daughter on the pretext that he does not marry off the younger daughter before the older one, and such a pretext will be of no avail before Allah Almighty." Salih Al-Fawzan said: "It is not permissible for a father to prevent the marriage of the younger daughter on the pretext that the older one must be married before her." The wali should be advised, and if he insists [on his refusal], the wilayah transfers to the next in line. If all [potential guardians] refuse, she may refer her case to the judge to arrange her marriage.