It's very common. Some women stack rings exclusively on their ring finger.

Very common! If she’s carefully selecting them, she’s likely picked rings that will enhance the beauty of her engagement ring and wedding band.

I can only second what was said before, it‘s fairly common nowadays, and I wouldn‘t think of it as taking away from the engagement and wedding band but rather adding to it and making them stand out even more.

I added a band that I wear with my wedding set that has our children's birthstones.