cellio | daf bit: Ketubot 80

If a man dies without children his brother is supposed to marry his widow but can decline. During the time that she is waiting for his decision -- that is, between the time her husband died and the time the brother either does or does not marry her -- she might come into the possession of property. Who owns it? If she were married it might belong to her husband, but she's in marital limbo. According to the mishna Beit Hillel and Beit Shammai agree that she may sell it or give it away and this is legal. This property is in the category called melog, property for which the wife retains the principal but her husband can reap proceeds (such as rents) during the marriage. Because the principal is hers she can dispose of it. (80b)