For the amount of comments she is making, I wonder if she is jealous.
My friend is a teacher who is, in theory, against private schools. She has also said if she could afford it she would send her own DC because she recognises the amazing privileges privately educated children get. And I get it, you can be against the theory of something but be jealous of the outcomes if that makes sense. I think I feel the same way about private schools, I’m not into them but the results do seem to speak for themselves. (Also, with people talking about bullying, my state school was rife with bullying and I was bullied relentlessly. I think that’s schools in general and a lot of teachers don’t care as much as they should, sorry).
She is either really, really, really anti private schools to the point where it consumes her that she needs to reference them every single time, or she is jealous.
Ifninwere you, I’d lay out in simple terms: Sister, we have different views and have made different decisions. I respect that you haven’t sent yours to a private school and that is your choice, however I have sent mine to one. I have heard your thoughts and I want to continue to send my DC to private. This needs to be the end of the conversation, I do not wish to address this subject with you again. Can we please agree to put it to one side?
If she doesn’t, I’d reduce contact. If she does bring it up, ignore it every time, don’t address it, don’t even acknowledge that she has spoken. Grey rock the subject completely and if she keeps on, then you can reduce contact.
But lay out how you feel in simple terms first.