It took Calidora mere moments to make an assumption based on the facts provided.
She could decipher what the message was instantly.
Flunra stated that Jessica attempted to kill Rex even though she was outclassed severely so that leads to one of the two scenarios. One is the culprit, wanting to tell Rex that he or she is coming for him, an act of personal satisfaction through telling him what is coming, before the arrival of his death.
But the method of using Jessica to try and kill Rex didn't align with the first scenario.
If someone wants to tell Rex that—there should be an aspect of seriousness in the method.
Attempting to kill Rex with Jessica conveyed impulsiveness, not seriousness.