Given what little I do know, I tend to lean toward the likelihood that my SIL may be unemployed or perhaps she is underemployed and embarrassed about it.
During dinner, she asked me what I do. I told her. It was a pretty straightforward dialogue. If the topic of her employment is off limits, then I'm not sure why she asked about mine.
If I had responded to her questions about my employment in the way she responded to DH's question, it would have been something like, "I'm aspiring to teach the world to sing in perfect harmony, and I'm retired from raising Sea Monkeys." DH was genuinely trying to get to know her, and he felt her response was dismissive.
DH has much stronger feelings than I do about our interactions that day with my brother and SIL. He believes they were downright rude the whole afternoon. I'm so confused by the whole situation that I'm not sure what to believe.