I've been on a few doctoral student admissions committees, this is my experience, others may have other opinions:
1. How hard is it to get into an American University PhD program with a foreign degree?
Not that hard. She will probably have to provide translations of her transcript and diploma, but we entertained applications from China, Korea, Turkey, eastern European countries, etc., no problem.
2. How hard is it for a international student to get funding in an accounting PhD program? I keep hearing on the boards that accounting is the degree with the most opportunity in both funding and jobs.
Let us hope that your young friend really has an interest in accounting research and doesn't just want a PhD. I saw that a lot too - young students with little to no work history who wanted a PhD because it was prestigious in their country and they didn't understand the nature of doctoral work in the US.
That said, most programs fund all doctoral students, native or international. We're not talking the humanities here - in IT, info science, accounting, business, comp sci (maybe a little less than previously), your friend should get full funding.
3. Would she need to do any coursework here, in the US, to qualify for a PhD program?
I can't speak for accounting specifically, for example, I don't know if you need to be a CPA, but for the other business majors, no further education should be required. Once her English is up to par, she should just apply to PhD programs and not spend a lot of time/money on courses to 'prep' for the PhD. That said, since she is here, she might look around at programs and see if she sees a gap in her knowledge, rather than just taking courses for the sake of taking courses.