Well, I have no doubt in my mind that the McCaskey's are filthy rich, but "net worth" includes assets. So if the articles states she is worth 1.2 billion (which I believe is low) that includes her stake in the Bears ( I have no idea what the breakdown is between family members).
Now, if they were to sell the Bears, they could get North of 6 billion. However, Uncle Sam comes a calling and takes half. Now you got 3 Billion divided by how many?
Not that it matters, but she doesn't reach billionaire status without figuring in her percentage in the Bears. She hasn't reached "billionaire status by investments alone, not yet.