Mouth shut sounds like a plan. Don’t engage. But if you did, don’t challenge or confront in any way. Maybe say, “I’m not sure what you meant by xxxx. Could you explain? No sarcasm, no irony. Or, “Thanks for your text. What I hear you saying is . . . then paraphrase the mean tweet giving her the most positive and generous interpretation, followed by - is that it?”
One aspect here that I've yet to think through is that it's a weird company insofar as it's small and entirely populated by seasoned veterans of the field who are mostly in their 50s and 60s, and then there's me, the young(ish--compared to them), inexperienced newcomer. I know she likes me, and I know she thinks I'm decent at what I do, so I want to think she think she's trying to mentor me in a way. But I think she's just not good at it. Anyway, I appreciate the advice. No one does it better than you.