Just echo what Hester said - that is exactly what happened to me.
I remember midweek, halfway through it all, said to my mum, this baby isn't coming out the way I planned - I'm going to end up with a section.
I wish I'd trusted my gut instincts then as if I'd elected a section at that point things would have been a lot different - I might have succeeded BF'ing for one thing.
I think there is a window of opportunity to a degree, where we have mental and physical capacity to see through a natural labour. But the more prolonged, the more intervention, the more inevitable a section might be.
I'll probably get flamed for this, but if you SIL is not as opposed to a section as I was, and if it goes on much longer and she starts to show signs of getting exhausted, teary and is feeling hopeless, it may be worth her taking control of the situation and opting for a section herself.
But it's DEFINITELY not at that point yet.
And i'm DEFINITELY projecting!