She'd get short shrift from me for some of her comments!
"DC just turned two and both parents are reasonably clever, so i won’t be surprised if DC is as well. But they says DC is toilet trained, except for when they’re not home, or for a poo, or overnight. So, not really toilet trained!"
I'd have said exactly that, possibly expanded into 'So not actually toilet trained in any practical sense, then?'. (Laugh at someone when they are preening - puncture their inflated ego.)
"They say their 2 yo is reading and send videos of their PFB saying some of the words (“Peepo!”) but not exactly reading, obviously."
Again, you do know what to say, you're saying it here
. 'You know that's not actual reading, right?'
"Our oldest (5) just had Covid and I said he’d sat in the lounge for two days and watched films all day, she glared and asked if I had thought about reading instead to keep him entertained because screens are so horrible for children’s development."
Oh don't be an arse! He was ill, didn't have the energy to concentrate on a story, watching a film was all he was able for. Do you insist your child concentrates on you when they are ill?'
"she’s still breastfeeding and keeps asking me why I’ve stopped and how my 2 yo must miss it and be sad."
'Give your head a wobble Sandra! You breastfeed for YOU, not your child's benefit. It makes you feel all Earth Mother and righteous.'
"She’s fully embraced “natural” living, no plastic allowed in their home. We were out at a park and she’d forgotten a snack, I had sliced berries in a plastic container and she said asked if the container had been through the dishwasher and she wouldn’t give them to her child because of the microplastic risk."
She does have a point about microplastics, but she's closing the stable door after the horse has bolted. It's everywhere and pretty much unavoidable. And there will be plastic in her home, again it's unavoidable. Was she sneery about you using a plastic tub? I'd have been sneery back about her not prioritising bringing a snack.
You may have noticed a theme in my responses. They're not actually about her PFB, they're about her. Her wants, her ego, her preening. Because her child is not the problem, her behaviour is the problem. She could be as PFB as she wants, it would only make me roll my eyes. But it sounds as if she is being judgey on top of that, which deserves a bit more than an eye-roll.
I think my default response to her would be 'Got your judgey pants on today, I see?'. I'd give her the benefit of the doubt (for a while, not forever) that she hasn't realised that she's tipped over from PFB/ProudMama into insufferable JudgeyPants/PerfectMama mode. If she persists (I can just imaging she well might, insisting she's only trying to help you to up your game from your slovenly standards <rolls eyes>) then I'd phase her out of my life.
If she takes on board that she's being judgey, the friendship can survive. If she can't (won't?) see that, then it's doomed - but you will have tried.