I think that suggesting she get a second a opinion from a doc who tries to avoid c/secs is a great idea. You took the words right out of my mouth. Here is the argument I have used repeatedly in my responses on this Forum: if the ob has c/sec surgery rates much higher than 15%, the maximum rate recommended by the World Health Organization and backed up by any number of studies, then you know you cannot trust the ob's judgment.
As for the chances of the placenta moving away from the cervix, I got this passage from here:
Placentia previa may be observed in as many as 1 in every 3 pregnancies before the 20th week of pregnancy. As the uterus grows, the placenta usually moves higher in the uterus, away from the cervix. But if it remains near the cervix as your due date nears -- which happens in about 1 in 200 pregnancies -- you're at risk for bleeding, especially during labor as the cervix thins (effaces) and opens (dilates). This can cause major blood loss in the mother. For this reason, women with a placenta previa are usually delivered by cesarean delivery.