The correct answer is B. As tenants in common, Emma and Rachel each own a distinct, undivided share of the property. This means that each tenant in common has the right to dispose of their share as they wish, including leaving it to someone in their will, without needing the consent of the other co-owner. Therefore, Emma does not need Rachel's consent to leave her share to Sarah. 

Key Point: Tenants in common hold distinct shares in property, which they can dispose of independently, unlike joint tenants who must act together.