My SIL has mental issues we found out about some time ago when she nastily verbally attacked my parents and myself over perceived slights.  Trust me when I say nothing wrong or mean was done at all...she is just not wired right and will take a normal benign interaction and make it something against her.  She has been dianosed with anxiety, depression and biPolar.  Usually problems happen when she is off her meds.  Her verbal attacks are quite vile and nasty.  

For years she has been halfway reasonable...my 80 year old parents, myself, DH (and my brother her husband) always bite our tounges and overlook things when she is rude or lashes out mildly.

Last week she went on a rampage against my parents and myself (found out after the fact she was off her meds).  I was working a part time job on top of my fulltime career (while DH is depoyed) and she knew ahead of time I would make it just in time for halftime show to see my nephew in Marching band after I got off my part time job.  But when I tried to sit down next to my parents in a seat they saved for me, SIL refused to move to let me pass and told me NO.  Said if I can't get to game on time then don't come at all.  She then got into it with my elderly parents when they said I have a right to come and sit with them to watch.  She then attacked my parents making ridiulous accusations against them, told us all to "rot in hell" and "f*ck off" and we are not allowed at nephews games anymore.   I started having flashbacks (like PTSD) of my evil SD and can't believe there are TWO people in my life like this. SIL left thank goodness.

The toll this took on my family is heartbreaking.  a few days later SIL calmed down and told my mother she doesn't know why she overreacted to me but it is all my mom's fault because SIL said my mom frequently gets mad at her.  THis is false, my parents are respectful and courteous to her...even helping and doing extra stuff for their family if needed.

My mom told me she and my dad are a mess (he has a bad heart), so mom sucked it up and apologized (yet SIL could not be specific on anything my mom did wrong).  Mom did this so they can spend their remaining years still seeing the grandkids and so we can all still have family gatherings.  My mom knows she did nothing wrong, but my brother said this is the only way there would be peace with his wife (he said he is leaving her in 4 years after the youngest graduates HS...he is misarable with his wife too).  My brother also told us, if we came to my nephews football games, she would see us sitting away from her and she would come over and make a scene...there is no reasoning with her. SIL is weaponizing her kids and holding our family hostage so we must give in to see our family.

I understand why my mom did this.  But I feel so upset and angry we have to take being treated like sh*t and my mom has to apologize so we can peacefully see my brother and his kids.  I know it is the only way we can see them and my brother knows she will make his life hell if he leaves her now (I think he is afraid of her actually).  At least when the kids are 18 they will have more freedom and can see us on their own.  I am having a hard time reconciling I have no choice in this matter.  I have had horrible things happen to me, am under great stress but don't take it out on other people.  Yet SIL makes all these excuses how much stress she is under, blah blah...and uses it as an excuse to treat our family like shi*t.  But here she is getting away with it because...the kids. If I behaved the way she did...for sure my family would not go that easy on me.  I'm not clear if SIL expects an apology from me, but I cannot stomach it if so. I however have no problem attending family events and only interacting with her if necessary.  This all was triggered after I rushed to see my nephew after working my part time job and made it in time to see him.  I don't see how that warranted a personal attack.  Unfortunately, I think if she ever attacks me again, my family would throw me under the bus for the grandkids sake. Nobody will take a stand against her because of the grands. Not quite sure how to deal with this.