I dont think the statement, "she should die", is a threat, a wish maybe but not a threat.
The legal definition of a "threat" is that it "must be on its face and in the circumstances which it is made, so unequivocal, unconditional, immediate and specific as to the person threatened as to convey a gravity of purpose and imminent prospect of execution." In other words, unless someone is threatening to do YOU real personal harm SOON, and you have reason to believe that they CAN and WILL do this harm, they're not legally threatening you.
So far as "defamation" is concerned...if what is said is true it's not defamation, if false it may be.
kiki