Sometimes the symptoms of depression may actually be, in part, for some people, kind of a side-effect of the drugs used for schizophrenia. I've heard that age 13 is regarded as very early onset for schizophrenia. I recall that it can occur early in childhood, too. The negative symptom effect, if it occurs, will take many weeks or months to begin to appear if the drug is sedating, by virtue of its side-effect profile. What you might experience early on is the sedation which sometimes is confused with the treatment effect of the drug.
Side effects vary depending on the drug.
My friend was symptom-free during her pregnancy. The question of treating a pregnant woman with psychotic symptoms comes down to an individual risk-benefit question. Whatever the statistics, it is common enough an illness that significant numbers of women, as well as men, are affected. We would also need to know if they've been treated with clozapine, which is the only drug that seems to have some specific efficacy for true treatment-resistant schizophrenia. In some patients, the psychiatrist may be able to use a combination of different drugs in order to optimize response.