How do you deal with relatives or friends who can suck all the happiness out of you?

My husband and I accidentally packed two very small minor presents for his family in my family’s basket. So Christmas Eve, we show up at his family get together and we are mysteriously two presents short. One family reacted the way you’d expect. They said it was no big deal and we could get it to them any time. They were surprised when we showed up a few days later. They didn’t think they’d get it back for several weeks because they live so far away from us.

The other family—the mother—my sister in law—went on the rampage. She chewed out my husband and me. Then she chewed out my mother in law (because she gave us the gift suggestion from a list of things she got from the kids. Had she not done this, the gift would have been “safe” in her baskets rather than in our unreliable family basket) She demanded that we stop everything on Christmas day and drive over to her house to drop it off before we went to see my family (we didn’t)

I was told that she just acts this way from time to time and most people in the family just weather it out and don’t take it personally. She never apologizes or admits she over-reacts. She just shows up one day at a family function and she’s nice to you again. I’d heard about this, but this was the first time I’d been on the beating end of the stick.

I don’t want to pretend this never happened. She went nuts. I don’t trust her anymore and I don’t want to be anywhere near her. Unfortunately, we show up at the same family events so we have to be together. How can I attend these events and family gatherings and not get angry every time I see her, knowing that she is either getting over some minor gripe or chewing someone out mercilessly every time I see her?