My ex
BF's mum was a nurse and she was in hospital after giving birth to her 3rd child when the woman in the next bed was told she had placenta previa.
It basically where the placenta is below the baby so when you go into labour the placenta comes out before the baby if you have natural delivery. The lady in the next bed was carrying twins and unfortunately one of them died cos of this condition. So its pretty serious and the midwife should be as helpful and supportive as they can. Hopefuly like Eamesy found it corrected itself if not they will discuss her options at the time but she may need to prepare to have a c-section.
hope everything goes ok for your sister