@Autumn567
Outrageously rude. I would be ghosting them tbh. Or at least giving them a VERY wide berth. On the rare occasion my own DM or MIL made a throwaway comment, my DH gave them a short shrift. And occasionally I would say 'please stop! I know how to look after my own daughter.' Not in a nasty way, just a gentle scolding way... But like fucking hell would I be taking it from some random neighbour.
If you can't bring yourself to ghost or distance them - next time I would say 'I have to say, you really shouldn't be commenting on my parenting, it's really rude and makes me feel like shit, and we'll fall out if it doesn't stop.' Don't worry about being 'rude' or 'nasty' SHE doesn't care about being rude and nasty to YOU.
And people do have a point by saying 'just wave quickly, and run in the house and avoid them' but this is going to be hard to do long-term. I think it needs addressing. And if she gets huffy and offended and decides she no longer wants to be friends.. RESULT!
WTF is wrong with some people?
Why do they think it's OK to comment on stuff like this? 
Their daughter in law has fallen out with them and they weren't invited to their son's wedding. They always said to us that she was "not a good woman", but now I'm not so sure. Apparently their son asked them to apologise to his wife once, but they refused.
Yep, it sounds like it's more about her than the DIL. Like in most cases, where a MIL and DIL fall out, it is almost ALWAYS down to the MIL. Not saying all MILs are shit by the way, as I am one myself, and many are lovely, but of the ones who DO fall out with their DIL, it's often the MIL's doing, not the DIL's...
The MIL is always the older one too (and often much older like 20 to 30 years,) so she should have more dignity, decorum, maturity, and common sense, but I know/have known quite a few women over the years, with dreadful MILs, and in every case, it's the MIL's fault.