There is a popular saying that beauty lies in the eyes of beholders. Someone could find it attractive whereas for others it could be somehow different. Broad shoulder is considered as a masculine feature which is why many don't like it on women. But, if broad shoulder goes well with other features, then it would be attractive for females as well.
Moreover, women with broad shoulders would be sturdy. Thus, they will not look dwindled or shrunken when they become elderly. They would be less vulnerable to fragility.