Can you just distance yourself from her, maybe see her without the kids?
I see a group of 3 friends whom I have known for many years, they live about 40 mins from us. We were the ones who moved away, 20+ years ago.
One is married with kids similar age to mine, the other two never married or had kids. One has health reasons which were, I think, the primary reason for not meeting anyone, the other has had a no. of long term relationships but never got to the stage of marrying or having the DC she wanted. All now in 50s.
She is lovely to the other married friend, who she is closer to, but over the years has made some very snide comments to me. Not regarding kids particularly, as she doesn't see them, but regarding what I wear ("when did you last buy clothes?" Has been said more than once. I only see her a couple of times a year, so its not as if am always wearing same outfit!!), how we holiday (caravan - bitchy comments about us caravanning), my running (if you carry on you may actually be able to run X race - a race I had already done a no of times).
We see the other family for a meal at either house once a year or so, always used to invite her and current partner to ours, but every time got told "I've no interest in playing happy families" or some such comment.
On us getting a dog "of my god how will you cope with a dog as well as kids" 😲whilst the other two friends were telling me what great news it was.
Christmas cards addressed to Kath and family (not even including DH name, she was with me the night I met him!).
I get that her situation must be hard, but I never understood why she was bitchy to me in particular.
I cant not see her, as I know it would be me cast adrift from the group, so I just suck it up as little as possible (xmas and Spring when we all have birthdays). Even then, I don't always make the move to arrange it. As well as the comments, it is nearly always me who drives to their area, probably a 80/20 split.