For what it's worth, I think your mother's attitude is shared by the vast majority of Indian-Americans, and even first-generation Indian immigrants like me.

In India, there are egregious things reminding you about it, i.e. literally every government form ever -- but in the US it's reasonably easy to ignore and forget about completely unless you go out initiating conversations about it, or are unlucky enough to run into someone like your friend.

I have had a ton of both Indian-American and Indian immigrant friends in the US, and have had zero conversations with any of them that involved discussing caste.