Definitely not a cultural thing at all. Just a choice.

My mom got our ears pierced and I will get my little ones ears pierced as well. I'm doing it for the fact that I think it's best so that she doesn't mess with them. If I wait and let her get them done when she's like 12 I have to worry about her keeping them clean, changing the earrings too soon... but if she doesn't like them when she's older, she doesn't have to wear earrings...

No. Multiple cultures do it. I've seen more African Americans and Caucasians do it than any other culture. Don't let anybody pressure you to do anything

If you want to wait that's your choice, don't let her pressure you. My husband and I decided at 2 months we would do it and honestly I'm glad because she didn't pull on them while they were healing. But if you don't think it's a good decision for your family don't let anyone decide for you.

I pierced my daughters ears as newborns.

I've seen all colors practice this. It's part of American culture.

I wasn't sure because my mother inlaw said it was and is pressuring me into getting my daughters done

As far as I know, I didn't know it was a thing because I grew up with all little girls ears pierced it wasn't until my husband said he wanted to wait that it was more of a heritage kind of thing after we talked about it.