E.D.
M.,
I so understand what your friend is going through, because I just went through one a month ago. Yes, it could take that long, though I doubt it will. With mine was the worst kind of cramping imaginable, and I thought I'd never stop bleeding, but I did. The benchmark my doctor told me to look for was bleeding through more than 2 super pads in less than 2 hours. If that's happening, then she needs to see someone.
She also needs to know that her next few cycles will be off. I was 10 days late starting my next period, and it was almost as bad as the miscarriage itself, with the incredibly painful cramps and heavy bleeding. But as time goes on, her body will readjust and she'll be fine and back to her old schedule fairly quickly.
I will definitely keep her in my thoughts, because I know how tough that is. I hope this helped.
E.