Unfortunately labouring with a baby in the posterior position mainly with a first time labour often women do get to 8-9cm dilated and then the last little bit wont go so a c/s is performed hours after being stuck at the same dilation. When an epidural in is use unless its one where you can be mobile even with synto it can be very hard to assist decent and rotation of the baby due to being stuck on the bed. You can try rocking the pelvis, being on all fours and a variety of other positions to aid with decent and rotation to help with dialtion but sometimes nothing works even with time there is no change. When the baby is posterior the part of the skull that presses on the cervix and helps it open up isn't as effective and a funny shape in comparison to the part that presents when its anterior (the most common and easiest way). When the baby is coming anterior (back of the skull seen first when crowning) its much more effective then when the forehead is presenting (posterior). Thats why birthing with a posterior baby is often longer and pushing is harder to get them out.
When a lady has birthed vaginally before the birth passage opens easier because its being used before and the cervix stretches more effectively and most of the time a woman birthing for the 2nd, 3rd etc time will not have much difficulty when the baby is posterior.
In the hospital setting it is not that common unfortunately for women birthing for the first time to have a direct posterior baby to not have assistance ie forceps, vacuum, episi, synto or c/s. Of course it does happen with no assistance and I have seen many but most medically based facilities have time limits and do intervene for a variety of reasons. I would guess its over 50% that have medical assistance.
I can understand your friend never wanting to go through what she has again and electing for a c/s next time. There is no reason the same thing will happen next time especially if her next baby is coming anterior. Me personally being a midwife I wouldn't take the risk either of perhaps it happening again and having another emergency c/s even when statistics are in favour of VBAC.