User blog comment:Stefan Salvator/Who ia more powerful?/@comment-4554525-20190802055150/@comment-4632123-20190802144505

The First Blade is useless if one doesn't have the Mark of Cain. So even if she gets the blade and stabs him with it, it'd do absolutely nothing.

I think Cain will win eventually, since as we seen with Dean, the mark can make the bearer immune to demonic powers, so he'd eventually be able to overpower her.

She could've killed him, yes, but the mark would just resurrect him as a Demon/Knight of Hell. and again, immunity to her powers thing.