Teach your daughter, that everyone is different, but it doesn't make it right.
There is nice and mean. I am sure your daughter knows the difference.
Tell her, some people are mean, some are not, but know who SHE is.
Don't let others affect her.
The other thing is: they are just car-pooling together. That does not make them BFF's. Especially for the older girl.
But being your daughter is younger, they don't see the fine lines socially.
But sure, the older one has attitude and denigrates your daughter.
So, if that were me... I WOULD right there, correct that girl. And I would tell the Mom that she is insulting the younger one.
It is not about comparing ethics between your family or theirs or about parenting.. but make it about how the older one is insulting the younger one. If the Mom asks how... then give examples but don't value judge what the older girl watches on TV etc. Because then those parents will not receive it well.
Or, you don't say anything. But if in YOUR car and this is going on... you TELL THAT GIRL... she is wrong. There is no reason to PICK on a younger child. Everyone is different and just because she watches shows like that or has a Justin Beiber party (ick), it does not make her better than anyone else. There is always people younger or older than her. And they ALL have different thoughts. I have heard kids like that.... at my kids' school, and I tell them "Oh yuck, I don't like Justin Beiber... you watch Austin & Ally? They don't look like smart kids they only worry about what others think of them. I'd rather be my own person....and think for myself."
I have actually told kids, that. In a nice tone of voice of course.
Teach your daughter, now... how to be her OWN person.
And to discern, icky attitudes and what a nice friend is or not.
I began doing that with my kids as Toddlers. So that once they started school... they didn't get too flustered over kids like that. And if someone was "mean" to them... they were able to just act like a Teflon pan, and be fine with themselves. Still.
Perhaps, you can explain that that older girl, is just a car-pool "guest." Not a friend or buddy.
And, not all "older" kids are mean to younger ones.
Some are though. So teach your child...
And not everyone has to like everyone.
Just be glad... your daughter doesn't have friends, like that! :)