L.A.
Two ideas:
First, work on volume. Practice what's a 5 (loud) to what's a 1 (whisper). This can be a fun game and will help her understand what those numbers mean.
Then when she's at a 5, you can say volume 3, to help her adjust her volume.
Second:
Give her lots of examples of what to do/say INSTEAD of the screaming. Be her voice and verbalize for her what she would be better off saying. Walk her through what you want her to be doing. You don't need to force her to repeat you, if that's causing her to be upset. Hearing you speak for her (and then respond as if she's said it -- and only after you've given the better way) will do more good than you think.
Model what you want her to do and treat her the way you want her to act.
L.