Just to also make the point that a CS in 1970 is likely only to have been an emergency. The experience of that is no way similar to now. I know that back then, being discharged from hospital after a day or so would have been unheard of after a CS. For an ELCS this isnt that unusal these days. Things have come a long way.
There is also a world of difference between the risks and the experience of an ELCS and an EMCS but for some unfathomable - and in no way completely ideologicalreason despite it being completely scientifically flawed to directly compare the two, they are constantly conflated and information misrepresented.
On top of that the way the risks of a VB are presented often neglects to include when the outcome didn't go to plan and you get medical intervention.
This distortion is fundamentally a disservice to women. Its shameful and yet is constantly done quite deliberately.
Its something that should provoke a lot more anger than it does, because its quite scandalous in how it misrepresents data to women.
Risk is not an equal thing either. Factors like how many children you intend to / are likely to have are often neglected. Age as well. And your underlying health.
If you are a first time mum close to 40, your chances of a vb without intervention are vastly smaller than a 20 year old gaving her second child. A woman having her first child at 40 is unlikely to have the additional risks of having multiple CS from lots more subsequent pregnancies too. A woman with infertility problems is unlikely to be having 4 or 5 C Sections (and accumulated risk with each subsequent pregnancy).
There is no one size fits all best way to plan to give birth, but there are definitely things that should be considered backed on personal circumstances in terms of risk.
Likewise having your first child at 15 has very different risks and considerations than having after having fertility problems at age 29.
The OP seems completely incapable of grasping any of the nuance or complexity.
Its just CS bad - VB good. And no interest in furthering understanding of shades of gray.
The OP should be doing this but its all about the need to 'educate' her sister.
How can someone with such poor understanding of the subject give any 'advice' of any meaningful quality to her sister.
The bottom line is she can't.
I really, really feel for the sister.