I was going to say the same as Emmy, posterior presentation can have an effect on the progress of labour - it can be very erratic with labour (and dilation) stopping and starting. My girl was sitting posterior for awhile and early labour started then stopped again and NOTHING happened for over a week. She flipped around before I was induced, but I could suggest it was a similar thing at play with your friend - the head not putting pressure on the right muscles to help dilation continue.