What would you do - telling a family member there is a problem with their child

My SIL and I have never really been close. She did a number of very purposeful things to ruin my wedding and this subsequently lead to a huge fight where we didn't speak for a year. We are now back on speaking terms and things seem to be okay.

I'm a Special Ed teacher. Three years ago I started to form a theory that her son has selective mutism. I only shared this with my husband. Her son is now in kinder and he is having problems, one of which is the teacher complaining that he never talks to her. At all.

Should I tell her of my theory? I want to try and stay out of this but my heart is saying I should do the right thing by her little boy.

What would you do?

Given you're a special Ed teacher, I think using that a little may help ease into the conversation. But I'm not sure how you'd go about it...

Can you have a basic chat with her, ask how he's going at kinder etc etc then when she says about the teacher saying about his speach maybe you could just say "ï've seen children like that who have issues with ..... " Maybe just lean into it from a professional angle - just say something like "not that i';m suggesting thats an issue but if your worried maybe ask your GP" ??

I told her... She phoned me to discuss how he was going and I told her what I think with a disclaimer that I'm not a medical professional and I am probably wrong.

She took it really well and seem to agree with me, so will have to see if she actions it.