Hi Sweetly,
I'd hate to see your SIL ruin Thanksgiving for everyone else in your family. I think I'd risk it, attend the event and keep a close eye on the two-year-old, not allowing your SIL to get near. At 8/9, I think your other kids are old enough to heed your instructions not to be alone with SIL. Plus, they'll probably want to hang out with any other kids anyway. If the kids peel off to entertain themselves, maybe you or your husband decide to "chaperone." Alternatively, maybe you insist the kids stay within earshot: "You can watch a movie/play a game any day, but today is a special family day and I want you to stay with me and socialize with your cousins." Maybe you give them kitchen tasks so you can keep a closer eye on them at all times.
If your SIL is that angry, chances are she might not even show up on Thanksgiving. If she does show up, maybe she'll behave because there are many witnesses. If she does have a meltdown, maybe she'll storm off, and the rest of the family can shake it off and continue with the festivities. If she becomes hostile to you or the kids, and if nobody intervenes to try to calm things down, you're free to make an excuse and leave, hoping to avert a scene. Maybe you "set the stage" for a possible quick exit by stating beforehand you have another house to visit that day, or that your toddler will need to go home early for a nap.
I know this is not ideal. I guess I've come to the point of being sick and tired bending over backwards, walking on eggshells and accommodating inappropriate behavior on holidays because of BPD. I guess my boundary is that when it comes to family, especially holidays which are about togetherness, I'm not allowing the pwBPD to isolate me. If she has a meltdown, she has a meltdown, and I let her go ahead and have one. I know it's hard on the kids, but so is isolating them from the rest of the family.
Just my two cents. Good luck, whatever you decide to do.


