"Not only did I love her, but I could tell the universe loved her, too. More than others. She was different. After all; I would be a fool not to notice the way the sunshine played with her hair." - Christopher Poindexter.
Maybe Clara actually was in the same universe as Sherlock and Mycroft at one point and she was their nanny and left that behind. Mycroft keeps it because she was the only one who really loved him for him.