but I’m worried as they get older and are able to comprehend that she might turn nasty and involve them.
So am I, OP. It's not like she hasn't got form for slagging off all & sundry, sorry, only half the population as she appears to reserve her ill-informed ire for females.
You have some great suggestion upthread, but I do understand it is hard to confront an ongoing, insidious problem like this - especially the first time.
However - & this IS meant kindly - you have inadvertently enabled SiL vile behaviour for nearly 2 decades, & that has handed her carte blanche to keep the digs up as if you deserved them. You also seem to have bought into the myth that YOU are some kind of homewrecker. You know you're not, right? Are you sure? Then why are you tolerating this shit?!
It's great that you have taken the first step by coming on here to air your views in preparation for making changes to SiL's toxic treatment of you. If you find the initial "speaking out" to her difficult, please remember that you don't have to be fancy. A simple "oh Gordon Bennett - are you STILL fixated on your tired old version of events?" & a withering look should suffice. Bear in mind PP's comments above about maintaining eye contact.
Bullies aren't used to being challenged, & tend to back down when it happens. Or collapse (which is what the tantrums are, effectively).
So you DO need to be prepared with a few key phrases.
But essentially it is simple:
- call her out on the ridiculous harping on
(oh DO shut up SiL, don't you realise how pitiful your obsession has made you)
- call her out on the inevitable subsequent tantrum
(oh dear you really do have a problem don't you. Have you consulted any professionals about your obsession, or are you going to go on letting it affect you like this?)
- set her straight
(you've fixated on this OW bullshit for 17 years now. Instead of continuing to make yourself ill & silly obsessing over it, why don't you have a talk with DH & I about what actually happened?)
Just keep maintaining is is HER problem & that YOU are gonna hear no more of it. Hence the perpetual, insistent use of the phrase "your obsession".
This bullshit belongs to HER, not YOU, & she needs to own it.