Sister

As you guys know, my sister is moving into a new house, newly engaged and planning a wedding, and today she is giving her notice at her job - hoping to start the great NEW job on Monday. Last night she had a horrible day; one of her bosses was yelling at her most of the day and just before she came home her boss REALLY gave it to her. I spent all last night at her house taking care of her and there's no where else I wanted to be. I am so grateful for a husband who lets me be there for my sister whenever she needs me. He is so great!
The thing is, my sister is the most wonderful, kind, caring person I know who never ever has a negative thing to say or do about anyone. Her biggest flaw is that her heart is too big. (Don't get me wrong, she's still my little sister and can annoy me more than anyone on this planet! And I annoy her too!) :-) Not only that, but she is a really hard worker, very efficient at her job as well as creative. She is amazing! To hear that her bosses yell at her all the time just makes me so angry. (Her bosses are husband and wife, not happily married, and will each task her to do something and yell at her for doing the other one's tasks first. They go back and forth all day every day for the past year and a half!!) Anyway, I don't know what to do with all this anger! I know her bosses lives aren't good, so I pray for them and that they don't take their unhappiness out on my sister. I pray that the Lord uses this to make Christina turn back to Him. I just keep praying and praying. It helps, but I still feel this anger in my heart towards them. I am so happy Christina can quit TODAY, but it's going to take a long time for me to forgive them.
I guess I'm asking all my sisters in Christ for advice on what to do with this anger (and get over it isn't an answer!). :-)