As long as the placenta is covering the cervix, I do believe a c-section is necessary for a safe delivery. It would be dangerous for the mom to push out the placenta before the baby, KWIM? I am definitely anti-cesearean in most cases, but in this situation, it is the safest way to get baby delivered.
When was her last ultrasound? Maybe the placenta has or will move by the time she is due. Many women have their placentas covering their cervix's at the ~20 weeks U/S and most of the time they will move up and out of the way by full term. Good luck to her.