I have a 'happy ending horror story' so I won't share it.
That said: pitocin causes the uterus to contract from ALL directions ((it's a naturally occurring chem in the body that is released after birth to start constricting the uterus. Meaning instead of a top-down squeeze (which is what happens naturally) it's all over.)) It is a LOT more painful than a top-down squeeze, takes a LOT more energy on the mum's part (because the muscle is fighting itself... like tug o'war... part of the uterus is pushing the baby UP and left, and right, and forward, and back, while only a SMALL part is pushing down and that 1 part is fighting against 6 other direction... and is almost *never* done without an epidural or major pain drugs. Because it takes sooooo much more energy to give birth this way women are encouraged to sleep through as much of their labor as possible (walking and movement encouraged with a natural birth, or early stages of an epidural birth, can wear a mother out and mean c-sect is unavoidable). Also, using pitocin greatly increases the chances of needing a c-sect (because it's not an efficient way of squeezing downward, some babies do NOT get squeezed downward at all, and many are squeezed so hard that the blood supply from the umbilicl cord -with oxygen- gets cut off, creating 'distress'. Babies naturally go into a *little* distress with labor, nurses and doctors expect it and are non-plussed. If the baby -under pitocin- goes into distress they do an emergency c-sect to keep the baby from dying or getting brain damage).
What pitocin is GREAT for is in cases like your sister's ... it's the "let's try it" option that can be done before a c-sect... so instead of having to head straight for a c-sect, it's possible to try for a vaginal birth.
Pitocin is admin'd in different ways. In many cases (planned inductions) it's just given at the beginning to try and "kick start" natural labor. In other cases it's given continuously. When done intentionally the most common protocols (protocols vary from hospital to hospital) is to try and kick start labor first, and if that fails to try a constant admin. If that fails, then it's time for a c-sect.
The biggest way one can help is by tossing all the "no problem" birth stories OUT the window. There is no 'skipping pain meds', no 'waiting to see if the distress calms down', no getting up and walking about when told to lay still. The moment an induction happens it is a MED PROCEDURE that I really wish people who had no idea what that entails would stop contradicting doctors who are trying to keep both their patients alive. No one has done it on here (yet), but your sis will get a LOT of grief from ignorant people about her birth.
As much as we plan our weddings and births... those aren't the important parts. The marriage is important, and the baby is important... the rest is just details.
Tell her she is going to be a GREAT mum.