Miscarriages are always incredibly sad. I once cared for a woman who had a miscarriage. It was her second pregnancy. (Her first pregnancy resulted in the birth of a healthy baby girl.) She was understandably very upset, and sadly I didn't help matters because I was the nurse who cared for her during her labour with her first. I knew that she would likely recognize me and it would just hit home even more that she wouldn't be walking out with a baby in her arms in a few months. Unfortunately I was the only nurse who could care for her, as we only had 2 RNs and the other was male (with the personality of a sledgehammer - I don't think he meant it but he wasn't big on tact).
I don't think it's a bad thing that she wants to try to get pregnant right away. In fact, depending on the cause of her miscarriage, the odds are good that if she conceives within the next couple of months the problem that caused her miscarriage will not occur with her next pregnancy, and she should have a healthy baby.
Our best estimates are that about 30% of pregnancies end in miscarriage, most in the first trimester and most due to genetic anomalies. We in fact don't know the exact number of miscarriages that occur, because a) some happen so very early the woman didn't even know she was pregnant and b) it sometimes happens that a woman will have a multiple gestation but lose one baby very early and have a second healthy baby. It appears to be a singleton pregnancy but it actually began as twins or more. My stepdaughter actually was a twin but her sibling died in utero and was reabsorbed.