What must a wife do who took money from her sick husband without his knowledge to buy land which she registered in her name, and her husband died before she informed him?

It is not permissible to take money from a husband's wealth without his permission. This is an aggression and a betrayal of trust, requiring repentance and seeking forgiveness, and returning the money to his heirs. This is based on the Prophet's (peace and blessings be upon him) saying: "On the hand is what it took until it returns it." It is obligatory to return the money to the estate to be divided among the heirs, unless the wife's legal share of the inheritance is equal to or greater than what she took, in which case what she took can be accounted for and deducted from her share.