Okay, yeah, this one is a bit of a doozy, so you might want to be sitting down . . .
FIL has joined a local chapter of a large organization. The kind mostly populated by old white guys who like to show off how rich they are. (FIL and MIL aren't, not really, but FIL can keep up appearances well enough and he likes rubbing shoulders with this crowd.) MIL absolutely hates being forced to socialize with them, but they have pretty frequent events for which bringing your spouse is strongly encouraged, so she's gone to quite a few. There's a fancy dinner coming up, and she wants to skip it, but FIL got really grumpy because she skipped the last one. He said she "wasn't being supportive."
The reason she skipped was because SIL1 was in the hospital having emergency surgery, having come home after living in a homeless camp a thousand miles away for the last year or so, and someone had to make sure SIL1 didn't up and walk out of the hospital as soon as she was mobile and SIL's kids aren't speaking to her at the moment.
But no, MIL is "not supportive." Not at all.