Either way, her best route might actually be to apply for a scholarship in a German university, they'd take care of the F-1 visa, all the legalities, etc., and she'd end up with a degree good for Europe and the US.
I'd say that a German degree would be as good as it gets.
Viadrina makes a hell of a lot of sense for Poles - on many courses, they get a "German" and a "Polish" degree for the same course.