Friend constantly talking negative about her own child

I have a friend that I’ve known for years prior to our pregnancies. Our sons are about 1.5 years apart, but are in the same preschool class. It’s been kinda sweet having them together because her son has known my son since he was born. But I’ve noticed that about the last year or so, she appears to be irritated by him. She will frequently talk about how annoying or ill behaved her son is- in front of him. I started limiting playdates. Then, the boys got super close at school and the play dates became more frequent. Still, negative conversation about her son… We recently had an outing with another friend and she acted irritated and miserable. She was constantly correcting her son… for what I considered “typical boy” behavior. They were a little rambunctious, but we were in an outdoor venue. I offered to take her son, along with mine, to allow her a “break.” She’s offended when I offered to bring her son along on play dates if she felt overwhelmed by the setting or venue. What did I do wrong? Am I the bad friend? What would you do in the situation?