Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is not permissible to take back a gift if it was possessed and accepted by the person to whom it was given. The Prophet (Sallallahu Alaihi wa Sallam) said: “The person who takes back a gift is like a dog which vomits, then eats what it vomited.” [Reported by Bukhari and Muslim]
Except for the gift which was given with the intention of compensation, and it was not recompensed by the person to whom it was given, then in this case one can take it back.
The evidence is what is reported by Imam Malik in Muwata’ that Umar Bin Al-Khatab (Radiya Allahu Anhu) said: 'Whoever gives a gift to a kinship, or as a Sadaqa, then he should not take it back, and whoever donates a gift with the intention of getting the reward then he can take it back if he is not pleased with it.'
Ibn Abbi Zayd Al-Maliki said in Al-Rissala: ‘The recipient of what is given for compensation has to pay its value or give it back and if it is consumed or lost, then the giver can ask for a refund.'
As regards the Hijab, it is obligatory to wear it in front of your cousin if he is not a suckling Mahram, when he becomes an adult or when he reaches the age of 13 years old and above.
Allah knows best.