Like button, which seems to have vanished from my screen here.
Many people begin PhD programs who do not complete them, even after having spent a year or two on them. I myself did that very thing, having been accepted into and completing about a year in a doctoral program.
Then due to other circumstances, (I had a serious illness and then later relocated with my family) I dropped out and never completed it. In doing my later resumes, I always listed my doctoral work under my educational credentials, (of course, never indicating that I did complete it and had the degree) and you know what, nobody EVER inquired about why I didn't complete it. It just never came up.
If they had wanted to, they could have verified that I did have the educational background and degrees I had indicated I had, (undergraduate and master's) and I assume that was part of the verification process. But as to "explain why this candidate never completed the PhD program" I don't think they asked this.
Unless your friend has just absolutely no other work or educational credentials to discuss or list on a resume, I can see why this would be a subject that isn't necessarily going to come up. Of course, it would be pretty much a complete deal killer as far as other doctoral programs. Apparently if she thinks she is going to be discussing it at length either on a resume or in an interview, she should practice on her interviewing skills.
I do agree that "she is a foreign student and so didn't really understand the rules" and always referring to it as "alleged plagiarism" is a huge crock of a worthless excuse. Anyone who begins a post graduate program of study is strongly encouraged to purchase and make use of the publications guide for their field, which clearly explains what is considered plagiarism.
No amount of "just being honest" and confessing anything, or particularly trying to argue about it or defend herself about the whole incident and saying she repents and has learned better is going to help her in any discussion. She should just avoid the subject if possible and be very brief about it if it does come up.