I had a 4th degree tear with my first birth so I can understand your friend's concerns. I too am pro natural birth and had a great induction 17 days post EDD, pain killer free and it was just on delivery that things went pear shaped. I was very unwell for a long time afterwards and also developed PND because of my post natal gyno issues and not being able to physically care for my daughter unassisted for a long time. It was a huge shock that it turned out that way. When I fell pg with DS I started to do a lot of research into the risks and options for birth post 4 degree tear. There are a range of issues to think about and discuss with your caregiver. Your friend is 6 months so there is still quite a bit of time to make decisions. I certainly didn't make my decision until I was about 36 weeks and it was my decision not my Ob. As my pregnancy was incident free he was happy to go with what I decided and had of course put elective CS on the table.
The statistics are over 90% on the side of having no major tears the 2nd time around. However, the consequences for having another tear can be quite severe, especially rectal incontinence. I read lots of fabulous stories online of women who went ahead with a natural labour and all went well. I don't think I came across one woman that had experienced a 2nd major tear. However, that is not to say they don't happen. For me, I decided to put my long term health and happiness on the table as being important consideration. I looked at all the possible consequences of having a CS and weighed them up with my experience after having DD. I am 43 and decided to have an elective CS. It was a decision I have been extremely happy with. I had a great CS, strange and different experience than natural labour, but it was drama free, I breastfed my DS in recovery within 50 mins of his birth (I chose my hospital on the basis that they allowed this and provided a MW in recovery) and haven't looked back. My recovery was factors better than the 4th degree tear experience, absolutely no comparison IMO. My bonding with DS was probably better and faster too TBH, but hardly surprising as I had the most awful traumatic time after DD's birth. I am still coming to terms with all those experiences and feelings after the tear, and as my second pregnancy progressed they all came back, very strong and I found it difficult to make any decision without considering my own mental well being as well as the physical possibilities.
The CS bloody hurt in the 48 hours afterwards. But the pain quickly dissipated and as I had planned to be off my feet, I had a great support network up and running and was able to spend 4 days in hospital toddler free, sleeping, bonding and generally having a bit of a babymoon/holiday that I wouldn't have had. It also gave DH time and space to help me and DS and bond well too.
One other consideration I had was when to have the elective CS. Lots of OBs want to whip them out before the EDD but I was very keen to go as long as possible, and it was my OBs suggestion (he is awesome) that I have him up to a week after my EDD as DD was so late. I ended up having a 4kg healthy boy 9/10 apgars 2 days after my EDD and he continues to thrive.
I wish your friend lots of luck in deciding and with her birth!