Well, number one, since they are PLANNING it, it isn't an "emergency".
Yes, if she has complete previa at 36 weeks, she will need a c-section. It is very dangerous to both mom and baby to try a vaginal birth at that point.
Has she had any bleeds from the placenta previa? If so, the "emergency" part might be if she has another bleed (or even a first bleed, if it is a bad one). With both vasa previa and placenta previa it can be very dangerous for the woman to go into labor - even a small amount of cervical dilation can result in hemorrhage and death of either the mother or the baby. I don't know much about vasa previa, but it sounds like that might be the more dangerous condition at this point.
Secondly, I can
NOT believe they would say "we have to cut you up the middle because you are too fat".

I do not know how overweight your friend is, or how far along she is. I can see, from a surgeon's POV, that a large fat pad that overhangs the pelvis would make a traditional bikini cut difficult. Perhaps as the pregnancy progresses, the fundus will push the abdomen out enough to not make it an issue?

In any event, the plan for a vertical cut COULD be because of the vasa previa, or even the placenta previa.
Did your friend have someone with her when she was told all this news? It might be helpful to have a friend, partner or other advocate with her at her next appointment. Someone who can be a little more objective, ask questions that mom thinks of ahead of time but might forget in the moment, etc. Emotions, IME, can cloud memory a bit. I really do hope they weren't as insensitive as it sounds.
