Her tearing sounds like it was quite severe. I am only speaking from my own experience. I Had a 4.5kg first baby with a 38.5cm head (and the little bugger had his hand up next to his face- just for added measure), resulting in 3rd degree tearing. My tears healed well, and no one ever suggested to me that I have a c/s for my next baby. I have quite a big frame though.
I was worried about my next births however as I had always heard that usually babies get bigger. For me though they got smaller (gestation got shorter, DS1 was 41+1, DS2 was 40 and DS3 37+5) and DS 2 was only 4kg resulting in an unsutred 1st degree tear, and DS3 was 3.5kg with only a graze.

Having said that, I think DS1 did plenty of damage, and I am now 8 years on, thinking I have a posterior vaginal prolapse.x

If she has the option, she should try to talk it through with a number of different midwives who can review her case and see what they suggest.