my sister-in-law accused me of undermining her parenting after I tutored her daughter, then her lawyer sent me a cease-and-desist

I (34F) have been married to my brother Tom’s world for as long as I can remember, but his wife Jenna (38F) has always been a different story. We’ve been in each other’s lives for about six years now, since they got married, and I’ve always tried to keep a respectful distance. But about three months ago, at a family barbecue, Jenna mentioned that their daughter Lily was really struggling with maths. She said it out loud, to the whole group, and I thought I was being helpful when I offered to tutor her. I’m a maths teacher, so it felt natural.

For a few weeks, it was fine. I’d go over twice a week, help Lily with her homework, and Jenna would thank me. Then last Saturday, we had another family dinner at their place. Everything seemed normal until dessert, when Jenna brought up the tutoring in front of everyone. She said I’d been giving Lily unsolicited advice about her education and undermining their authority as parents. She claimed I told Lily to ignore their rules about screen time. I was floored, because I never said anything like that. I just helped with algebra.

Later that night, I saw her Instagram story. It was a vague post about “people who can’t respect boundaries as parents” and she tagged a few mutual friends. The group chat exploded. People were taking sides, and I tried to defend myself, but Jenna’s allies drowned me out. Tom stayed completely silent. I felt like I was drowning in their words.

A few days later, a mutual friend named Sarah sent me a screenshot of an older group chat. It was from six months ago, and it showed Jenna specifically asking for my help. She wrote, “Mia, can you help Lily with her maths? She’s really struggling and I don’t know how to teach her.” I felt a wave of relief, because the proof was right there. But before I could even think about sharing it, I got an email from Jenna’s lawyer. It was a cease-and-desist letter, threatening defamation action if I posted the screenshot publicly. She claimed it would damage her reputation.

I was terrified. I didn’t know what to do. I just wanted to clear my name, not tear the family apart. But how could I defend myself without breaking the law? Tom finally called a video call with me and Jenna yesterday. He looked exhausted. He mediated a truce, where I agreed not to post the screenshot, and Jenna agreed to take down her Instagram story. We set a boundary that I won’t be involved in Lily’s education anymore. But it still feels fragile. Jenna hasn’t spoken to me since the call.

Am I overreacting? I only did what she asked me to do.