They certainly made their money from US Citizens.
I don’t know specifics, but I’d guess they made their money in a lot of countries.
If she is a nonresident alien with US source income, she could very well be subject to tax. But if she’s not an American and lives outside the US, I think different rules apply. I would think it depends who signed her, where they’re based, and what tax rules they’re under; because they pay her salary. As with anything, “it depends.”
He produced ACDC's albums, an Australian band that outsells Shania Twain. He was rich and famous (in his own way) while Shania was still a lounge singer.