To make matters worse, she gives any mention of my own kids a short shrift.
How often do we hear of this on MN - somebody doesn't want to hurt somebody who's doing something unreasonable, yet the person doing that unreasonable thing has no such qualms about upsetting them in return.
Can you challenge her as to why she tells you so much about her kids but then blanks you when you say anything to her about yours? It might help if, in the run-up to challenging her, you persist doggedly and shamelessly in relating the most tediously dull things about your own children for a long time, every time you see her, obliviously ignoring all her attempts to shut you down, but all the while making a mental note of her reactions to use as ammunition.
Actually leaving the thread can cause a lot of ill-feeling that you may not want to do - however innocent and noble your reasons, people will see it as a massive flounce and a gross snub to them as people - but you can always just mute the thread and ignore it.
If she asks what you thought of her latest post or asks why you don't reply, you can quite reasonably say that you're having to scale right back on your WhatsApp usage in general as it's started to demand so much of your time with constant new messages on so many groups well, hers, anyway that you'd never get anything done if you jumped every time it beeps (or you've switched off notifications). Maybe your boss has noticed it and made negative comments....
Tell her that you scan through it periodically and read any work ones but otherwise assume that people will call you* about anything urgent or important. You often don't notice things until the conversation has moved on and the moment for adding to it would have long passed.
*This is one problem with no-effort mass spam communications - nobody would ever take the trouble to call somebody just to tell them how funny it was when their toddler was dancing to the telly, but they'll film it and stick it on a WhatsApp group and send it to everybody they've ever known without a moment's thought.