Her body will know what to do. They have been doing it since mammals evolved, and the vast majority are uncomplicated. As long as she follows basic precautions, a woman should be fine. Dangerous pregnancies are the exception, and even some breech babies can be born the normal way. Pregnancy and birth used to be dangerous because of bad conditions, but that is not the case anymore.
In most cases, pregnancy is completely safe without maternal doctor's visits. In many countries and indeed until relatively recently in our own history, women have been pregnant and have given birth without any doctors intervening. Of course there are always cases where intervention is necessary but these are in a minority and for the average woman, doctors visits are not an essential part of pregnancy.
Yes, pregnancy is safe without maternal doctor's visits, because most of the time, the women will not have a problem. Childbirth without assistance would be more dangerous. But in terms of a pregnancy, the woman is not sick. Childbirth and pregnancy is something that happens naturally in nature. You don't need a doctor for what happens on its own.
Pregnancies have a chance to become complicated, and doctors are qualified to pick up on early signs of problems, complicated birth defects etc.. It is important that women are adequatedly monitored and regularly visit a doctor during their pregnancy to ensure that they are safe, healthy and steering clear of behaviors that could harm the unborn child.
I myself would want to know that I was pregnant. You could put the life of your child at risk by not having the proper medical care. I was very sick with my son and went into preterm labor and did not know it. If I did not have a doctor appt. that day, my son and myself could have died. I was able to go and the doctor knew that I was having contractions. I was given medication to stop them, and the rest of my pregnancy went as planned. It could have ended very badly