It really depends on how far along she was and if she had have a D&C. If she was less than 6 weeks and passed it on her own, then waiting one cycle is best. Otherwise, waiting two cycles would be better. I highly recommend she get the book Taking Charge of Your Fertility and start tracking her cycles and watching her temps and cervical fluid. Not only will it help her achieve pregnancy, but it can also help her understand any repeat losses if they occur.
I have had 7 m/c's. I have one beautiful baby girl for whom I went to the fertility dr to achieve. I got pregnant last month and lost it at 5 weeks. Since it was not that far along, I passed it on my own, and I didn't bleed that much. It is fine for me to try again this month. I know that my lining was not thick enough to carry the pregnancy based on the fact I bled very little for 3 days. I know how to increase this, so I am taking the supplements now and will probably wait one cycle before I try again just to make sure.
I'm so sorry for her loss. If she needs someone to talk to.. send me a note. I'm fairly an expert at the charting thing.