Ketubot, Chapter Eight, Mishnah Six
This mishnah appeared word for word in Yevamot 4:3. I have replicated my commentary here for convenience sake. Despite the fact that this is its second appearance, it is likely that it was first taught in this context, where it matches the literary pattern of the rest of the mishnah. Only later was it brought to Yevamot.
1) If a woman awaiting yibbum came into possession of money:
a) Beth Shammai and Beth Hillel agree that she may sell it or give it away, and that her act is legally valid.
2) If she dies, what shall be done with her ketubah and with property that comes in and goes out with her?
a) Beth Shammai says: the heirs of her husband are to share it with the heirs of her father;
b) Beth Hillel says: the property is to remain with those in whose possession it is, the ketubah is to remain in the possession of the heirs of the husband and the property which comes in and goes out with her remains in the possession of the heirs of her father.
Section one: Beth Shammai and Beth Hillel agree that a shomereth yavam can sell new property that has come into her hands since the death of her first husband. She does not need the permission of the yavam, because he has not married her.
Section two: If she dies, there is a dispute between the two houses concerning her inheritance. Usually a husband inherits his wife, but in this case she only had a yavam who had not yet performed yibbum. He is not fully her husband.
Beth Shammai holds that the heirs of her husband, meaning the yavam who inherits from his dead brother, splits the money with the heirs of her father. The heirs of the father inherit since an unmarried woman is inherited by her father.
Beth Hillel does not split the money evenly. Rather, each part of the inheritance remains where it is presumed to be. Since the ketubah, meaning the money paid from the husband to the wife upon death or divorce, is still with the husbands estate, the husbands inheritors collect this money. The dowry is in the wifes possession, since the husband cannot sell it. Therefore the wifes fathers inheritors inherit this property.