Emeraldia didn't recognize Might Guy when she killed him
That might explain why she sounds shocked when she hears of his death, and as of Chapter 7, is determined to find his killer. Thanatos is one of the five villain's in Madara's team
Rose said she wanted to have Thanatos in the chapter where Madara explained his plan, and Madara only said four of the people on his team instead of all five. Besides, she seems to want to us to make guesses about Thanatos, so I might as well.