User blog comment:Zathronas/Analysis by an author: "Gold"/@comment-15108745-20131226184438/@comment-10380701-20131226231623

We never did know when Summer Rose died... for all we know she died when Ruby was like 3 or 5 or whatever.

The younger you are, the less impact a relative's death tend to have in a long while. There's the feeling of loss, but children have an easier time to cope.

It helps that Yang is being Yang to Ruby.