Without getting too deep into your SIL's medical issues, are there triggers for her aggression? Are her outbursts completely without warning or can people who know her well kind of see her behavior deteriorate? Many times these behaviors have situational triggers or can be related to medication related issues (too much or too little, missing doses, etc...)
If your wife tells the family that she is not welcome in the home, will they respect your wife's wishes? Making this a legal issue without exhausting the possible internal family options may be counter productive. Obviously the safety of your wife and immediate family members is paramount, but as long as you and your wife want to maintain a relationship with your SIL, you will always have to deal with the potential for her aggressive outbursts.
Family stuff can be messy. I hope your wife wasn't seriously injured and she takes precautions to prevent further violence against her and other family members. I can only imagine how frustrating this is for you. It is yet one more sacrifice you and your family are making for us. Thank you for your service.
Be safe.
You want to be a martyr, I want to make you one.
Has she been actually diagnosed with mental health issues? Is she on medication for them? You could always call CSPD and if they evaluate her actions and determine that they have probable cause they can put her on a mental health hold. That way she would A) Be separated from causing problems for up to a few days and B) She could potentially get some help/medication for whatever is going on with her. Just a thought.
This is a tough topic, because our current laws don't let us commit people who are out of control, these things end up by default in the criminal justice system.
You need to get your wife on the same page as yourself. It can't be true that your parents-in-law are ignoring your wishes, your wife must be undermining the message of not bringing the sister with them.
That's pretty damn disrespectful of her parents, to not do anything or (it sounds like) even acknowledge that there's a problem. Worse, since your daughter is exposed to it. We have some similar issues with my son (he's high functioning autistic) but with him there are, as mentioned by cstone, triggers so we can see it coming and usually head it off.
It sounds to me like the best thing to do overall, and probably a hard one for your wife, would be to make it clear to the in-laws that your sister-in-law is not allowed in proximity to your wife and daughter...and since they have proven that they will not respect those wishes, neither are they until they can either respect them or get a handle on the daughter in question. Mental issues or not, this is a question of safety, both physical and psychological for both your wife and daughter. It sucks that the end result, at least temporarily, is that your wife wouldn't see her folks and your daughter wouldn't see her grandparents for a while, but maybe they would finally understand how important the situation is. I can understand how your wife could be reluctant to do this; but it isn't just her...your daughter is involved too. If they won't do anything about the problem, then don't let them near. If they come over, don't answer the door. That sort of thing.
I had to put my foot down with my mother regarding my daughter when she wouldn't respect our wishes (hell, requirements) about what she fed my daughter when she'd watch her and some related issues...my daughter was a preemie and had certain issues that my mother blithely ignored, convinced she knew better than we did. We had a huge blowout, and it ended with her screaming at me that "I couldn't tell her what to do with her granddaughter"...uh,....WRONG. I told her she could see her again, and MAYBE start caring for her again, when she would respect our wishes, and why. Took 6 months. But it was worth it to prevent something worse from happening. Had issues with my MIL involving her worthless (and now late) husband, my wife's stepfather. Same thing, we had to limit her contact with the kids to only when we were with them, and outright ban any contact they had with him. She whined and bitched and finally, listened. But, she's a whole 'nother story.
I know from experience how frustrating things like this can be, and while you're deployed (I am, too) it makes them that much harder.
Stay safe.
SI VIS PACEM, PARA BELLUM
Herding cats and favoring center
It's pretty simple to me, but I know it will be harder for your wife. She has to cut off her sister completely and if her parents will not respect her wishes, they have to be cut off completely also. It's the only thing that works, but it's going to HAVE to be your wife that drops the hammer on it.
Mom's comin' 'round to put it back the way it ought to be.
Anyone that thinks war is good is ignorant. Anyone that thinks war isn't needed is stupid.