Praise be to Allah.
A woman may adorn herself for her husband in various ways and uncover her charms before him at any time, because he has the right to enjoy intimacy with her.
With regard to what you have mentioned about doing that inside the prison, there is nothing wrong with that, subject to two conditions:
1 – That no stranger (non-mahram) can see the woman, either directly or through surveillance equipment.
2 – That this does not have a negative effect on the husband, such as provoking his desires and inflaming his emotions, or causing him to compromise his religious commitment and give up his adherence to the truth that he is following, because he wants to get out and go to his wife and children. Allaah has warned us that our wives and children may be a source of fitnah (temptation) who may prevent a man from doing that which Allaah has enjoined upon him. Allaah says (interpretation of the meaning):
“Say: If your fathers, your sons, your brothers, your wives, your kindred, the wealth that you have gained, the commerce in which you fear a decline, and the dwellings in which you delight are dearer to you than Allaah and His Messenger, and striving hard and fighting in His Cause, then wait until Allaah brings about His Decision (torment). And Allaah guides not the people who are Al-Faasiqoon (the rebellious, disobedient to Allaah)”
“O you who believe! Verily, among your wives and your children there are enemies for you (who may stop you from the obedience of Allaah); therefore beware of them! But if you pardon (them) and overlook, and forgive (their faults), then verily, Allaah is Oft-Forgiving, Most Merciful”
‘Attaar ibn Yassaar said: All of Soorat al-Taghaabun was revealed in Makkah, apart from these verses, which were revealed concerning ‘Awf ibn Maalik al-Ashja’i, who had wives and children, and when he wanted to go out for jihad they wept and tore at his heart, and said, “Who are you leaving us to?” He felt sorry for them so he stayed, then this whole verse was revealed in Madeenah concerning ‘Awf ibn Maalik al-Ashja’i.
Al-Tirmidhi narrated that Ibn ‘Abbaas said, when a man asked him about this verse: Those were some men from Makkah who became Muslim, and they wanted to go and join the Prophet (peace and blessings of Allaah be upon him) [in Madeenah], but their wives and children refused to let them go to join the Prophet (peace and blessings of Allaah be upon him). When they finally came to the Prophet (peace and blessings of Allaah be upon him) they saw that the people had learned a great deal about Islam, and they wanted to punish (their wives and children), then Allaah revealed this verse. This was classed as hasan by al-Albaani in Saheeh al-Tirmidhi, 3317.
We ask Allaah to make His religion prevail and to relieve the distress of our Muslim brethren, for He is Able to do that.