so did Helen want Sam to actiually shoot her sister??

I find Helen and Fred scene a key point that help you understand Helen behavior.
When Fred leave Helen, he tell her she don't have any heart anymore and beg her to change "Why can't you, Helen, before it's too late?" although he remains skeptical about her ability to return to a moral life. For a few moments the shocking from Fred statement (The voice of reason and morality in the story) make her do the right thing and call the police.

Than from the moment the sister tell her she didn't give her any money the old Helen back to life and we see a vengeful and greedy woman. Georgia tell her in very clear words "You won't get another nickel from me as long as I live. And when I die you still wont. I'll see to that first thing in the morning". In other words, if she don't kill her today, Georgia change her will first thing in the morning without giving her any money.

This's the reason why she wants Sam shot her sister, unfortunately for Helen her inability to change results in her death. Just as Fred warned.