The way I see it, you get to an age (especially once having kids), where you turn into a mature adult. You put up & shut up, or you say something & walk away. I've known twits. Plenty of them. But I usually listen to the crap, roll my eyes to myself, maybe let them know my thoughts on whatever it is they wanna winge about & get over it til next time.

If she has a racist comment, you could always tell a little white lie that might make her rethink the things she says to anyone & everyone. I do this when it comes to extended breastfeeding Its not a lie though Just makes them rethink their big mouth.

She will not learn how to get along with the general public if noone tells her she's saying the wrong things. Let her know it offends you & she may or may not learn from it. If she doesn't, maybe just be polite but stand offish IYGWIM. Don't engage in conversation other than short answers that might make her see you're not too interested.

Anything is better than the immature high school crap these girls are carrying on with. Just because you're 'putting up with her' on the train doesn't mean she needs to be in your lives. Its only to & from work is it not?

Maybe ask those girls how they'd feel if something happened to her due to depression after being treated that way by them? The way they're acting may have a bigger impact than they think...