I had a vba2c and I can only say , she ABSOLUTELY has to believe in herself , she can do it . Everybody told me , that it´s impossible to do , and that I´m playing with my life and that of my baby !
B....s...
,the risk is soooo much greater with a repeat c/s !
Tell your SIL to get all the information she can get her hands on , all the studies vbac versus rcs , the percentage of babies dying or having problems after uterine rupture with vbac (appr. 0,2 %) versus the the risk of mother and/or baby dying or having serious health problems after rcs (appr 1,7 %) and so on , all he successful vbac birth stories she can get her hands on , a great supporter , not necessary a Doula (even though that´s ideal) but at least some strong-minded person , that will throw herself between your SIL and the doctor , somebody who keeps her focused on her goal of vbac .
She has to make sure , that everybody in the delivery room knows , that c/s is only an option if there is a definite need for it .
I was in really slow , gentle labor for 4 days with my vbac , then on tuesday late afternoon , my water broke (by itself) , then everything picked up and I dilated from 6 to 10 cm in about 1 hour and my son , who was still tossing and turning around inside of me , took a dive , I could literally feel that , and popped out . I think , that "you have to dilate so and so quickly" is stupid , our bodies know . what they are doing and I firmly believe in my case my body knew , that it needed that loooong , gentle labor , so that there was not so much strain on my scar .
Plus , if baby and mother are doing well , there is no need to induce , after all , do doctors automatically induce a first-time mother , once she hits the 40-week mark ? NO !
So , tell her to find a really supportive doctor , not one that apparently just tells her , what she wants to hear and then does what he wants to do ( c/s)
and tell her , not to let anybody rush her .
After all , nobody has the right to say "we won´t allow that" , she is an adult and she can make that decision , and that´s why it´s important to get all the info possible .
It helps for her own sake , too
I read every piece of paper I could on women having vbac´s and I thought , if they can do it , so can I .
And so can your sister-in-law 
Follow Mothering