I just had a 4.8 kg baby eight weeks ago and suffered a fourth degree tear requiring stitching in surgery. fourth degree tears come with with a subsequent risk of faecal incontinence, prolapse etc etc.
I was told by one health professional that any future babies would need to be born by c section while another told me that is not necessarily the case.
I'm not planning on having more children but if I was your friend, I agree with above and would get multiple opinions from various health professionals ( OBs, pelvic floor physio and so on) and seriously investigate positioning during birth and would keep an eye on the size of bubs.
However, even having done all that I am sure there would be a risk of tearing again and it would be a personal choice to pursue a vaginal birth.
From a purely personal point of view, I wouldn't want to risk faecal incontinence and one fourth degree tear was enough for me and my poor pelvic floor.