I also had a 4th degree tear with lots of stitches and know how she must feel... poor lady!!! Honestly, the excruciating pain was there for about 4 weeks, was downgraded to strong pain for another 4, and then slowly got better. It took many months until I was pain-free. I was given this medication called Voltaren in the beginning but it totally knocked me out so I pretty much got by on ibuprofen and lots of teeth-clenching.
What helped me most in the beginning was basically avoiding sitting at all. I think I spent the first 8 weeks lying down or balancing on one butt cheek. When I peed, I took a pitcher of warm water with me and poured it out as I peed to neutralize the sting. I took several sitz baths a day with a tannin-based powder which has a similar effect as witch hazel and kind of dries out the wound area. Then I'd blow dry myself down there on a low warm setting for about 5 or 10 minutes.
All the best to her... I hope she is able to enjoy the baby despite the pain!