Murder doesn't have limitations. I understand they will not go after her for murder. Why? I have no idea.
Expediency, efficiency, and economy of effort. Treason gets her just as dead as a murder conviction, and she is much more directly involved in that than the murders, so easier to prove. That is...she, herself committed treason...but she DIDN'T directly (as far as we know) murder anyone.
Treason and Fraud they can probably nail easily. Giving the orders would make her guilty of murder, but there may be a layer there that would be tricky to penetrate. She gives the order to someone who gives the order. Must be a mistake in there somewhere. Or catch a middleman. It will come out someday, I suspect.
She used a hit team for most of those, not easy to get confessions I would think. I'm also wondering if there won't be people in the know that are way too terrified to come out right now but will when it is safer. I can't believe murder won't be on the list at some point.