@Nihilist
There's no point arguing this , he has forced her to do his bidding before. Admitted by Death itself. If this was just a run of the mill thing, she wouldn't have felt so slighted by it. The fact that she was humiliated and stated it should tell you it wasn't a "normal" occurrence. He forced her to do something against her will.
Plus back on topic, there's more than one way to "kill" something if you are creative enough. The Cocati, or whatever the correct spelling of the name of those plant like things that were in the Silver Surfer issues that were chasing after Manits, killed an Elder of the Universe. When he told them that he couldn't die, they responded back, "Death isn't part of your destruction".
I'm also guessing anyone that can "nullify" or erase a person from existence can do it too.