What is the ruling regarding the action of a wife who receives money from her husband to distribute it for charitable purposes, and allocates it to her needy widowed sister without her husband's knowledge?

A wife who has been authorized by her husband to manage money is not permitted to act outside the scope of the authority granted to her by her principal. If she deviates, her action is invalid unless approved by the principal; otherwise, she is liable.

Therefore, what this woman did by giving the entire amount to her sister is a clear error. She must repent to Allah. To rectify this, she must either disburse the money to the parties specified by her husband, or inform him of what she did. If he approves, there is no sin. Otherwise, she is liable for what she overstepped and must return it to him.