How do I deal with my in-law's rude 11 year old daughter?

[Sarah2116]

Oh my gosh, I'm so freaking aggravated that I'm ready to grow 3 heads and have my scorpion tail shot out spikes. Last night I got onto my sil who is 11. She is always getting on or yelling at my 5 and 3 year old daughters. Not only that but when she plays with them its more like she just teases them with something and refuses to even let them play with the item. Well I had to go over to get my girls, because my husband was taking to long at his dad's house. I get there, and the first thing I'm seeing is her yelling at them. I told her to stop and to leave them alone. After I left my husband told me that his sister was "crying her eyes out". So of course my husband's father took him outside to ask what was wrong with me and why was I always getting on niki. I'm pregnant with my 4th child, and they think that I'm depressed because of it. Well I later find out from their adpoted daughter, that as soon as her dad and my husband went outside, she goes to her mom, who of course babys her, and then tells her mom that my girls deserved to be yelled at and that they are brats. So of course my husband comes over and is getting on me. which totally pisses me off, because he did nothing, the only time he said anything, was to apologize that the girls like to rough house, what kind of BS is that. Then he tells me that he thinks I'm going crazy from taking care of the kids all day. Errrr. I could really go over there right now and show them what clinical depression really is!!!!!!!!