Thank you all for your condolences, support and knowledge. We have identified and came to the conclusion that a Coyote jumped over our back brick wall, attacked and killed her.
We found a deep, large print where the coyote landed when it jumped over a 7 foot brick wall. We also found "skids" in the wet grass where a chase occurred as well as small tufts of fur that had blown into the corner of the yard.
We live in Frisco TX and if you google "Coyote Attacks Frisco TX" you can see what an issue it has become. I know that we (humans) are invading their space and have no harsh feeling toward the coyote simply for being a coyote and hunting for food. They were here first. I just wish it would have stuck with rabbits instead of our precious Blue Bell. Our twin 7 year olds were and still are devastated.
We will miss you sweet baby blue.
Pictures below of paw prints