Hi Kate,
Possibly this refers to a hidden desire you may have for achieving/ accomplishing something that you feel that your sister in law has achieved. Possibly you feel that the opportunity for accomplishmeng this important goal of yours has slipped between your fingers and that you have missed your chance to accomplish it. However, God is a redeeming God and a God of “second” chances. All things things work together for good to them that love God, to them who are the called according to his purpose (Romans 8:28). When we give our lives over to God, no experience is wasted. He makes all things beautiful in its time (Ecclesiastes 3:11).