If thats the case, with such constant proximity to Ai-Kun (which almost certainly a vajra hatchling), I am suprise Ranka has NOT gotten the V-virus. Another possibility is that Ranka's part Vajra or at the least, her blood is immune to the V-virus.
At least now Sheryl is no longer influenced by Grace, don't worry guys, Sheryl is a strong girl, she would come back and show Grace she is a survivor and won't give up easily !