@UranusAndNeptuneAreJustCousins No, it's set several years later. Not immediately after.
The theory that the crystal shortens your life is just that, a theory. They don't have any evidence that it shortens your life, only that it's painful to use. But wasn't painful enough to discourage a romantic magical broom ride.
You have no idea that Sophie was actually even killed. She just falls after failing to match Izetta's spirit bomb. Not once do we get a confirmation of her death, especially whether or not it was the crystal's life draining that caused it. You also forget that Sophie was literally just a clone that was set to have a short life span anyways. The original Sophie used the stone much longer than the clone and Izetta and lived for decades until she was betrayed and executed.
So in short, yall don't know what actually happened.