All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The Mahr (bridal gift) is an exclusive right of the wife. Whenever she takes possession of it, she has absolute right to dispose of it in any lawful manner she wishes as we have already clarified in Fatwa 59310.
Therefore, if the husband gave his wife money to buy gold and she instead used the money and did not buy gold, then she has the right to do so. However, if she had consulted her husband out of respect for his feelings, this is good, and it consists of good manners.
Allaah Knows best.