Yep, I have a rear facing 20 month old. I also have my 4 year old in a Britax that goes to 80 lbs., so he will be in a car seat (not booster) until then. I don't drive my dck, but if I did, I would have to be able to afford Britax or Graco seats for all of them (I probably have enough already as we have 4-one for each kid for each car, my mom has 2, and my mil has 1) and would have to have the space to rear face all kids under 40 lbs. or at least until age 2. It's not worth it to me. I make their safety a top concern in all other aspects of our day, so why would it be any different in the car? It really bugs me that I have one dc mom who keeps telling me "The day she turns one we are turning that carseat around, if not before." This mom has been in at least 4 car accidents that I know of (including a rollover) and her baby has already been in one with her. It just wouldn't be worth it to me as a mom, and as far as liability goes, as a provider either.
However, as far as know it all moms, that does get annoying. Is there any way you can do the old "smile and nod" approach and do it your way when she isn't there? I don't mean as far as safety, etc. is concerned but maybe remove the teething necklace/not wear the baby/use an occasional disposable if necessary/etc. I must admit, I've been guilty of this before.
The one that especially gets me is the baby wearing. It is especially difficult if they hold or wear the baby all the time and co-sleep and never let the baby cry. It's not that I disagree with this type of parenting, it's just that the baby usually requires a lot of care/holding/physical contact in the daycare setting and it's just not very practical. They usually don't sleep well either because they are used to physically touching someone all of the time. It's nice and all, I just can't do that here, and I think it is just fine to encourage some independence from a baby here and there.
And it's true that not all moms like this are know-it-all and annoying. I've been a breastfeeding, organic food mom, too, and I consider myself quite normal.