This check is performed when you're not sure how a young women will look when she gets older. This will give you a window as to how well the women will age. You can look at her mother to determine several factors. These factors include but are not limited to: weight, build, size and mass.
I understand that you are interested in marrying Sally. However, have you completed a Mom Check? I saw her mom the other day and her figure was less than desirable.