I do not know the standards of assessment with oil and gas industries. What I do recommend is to get a functional capacity evaluation (FCE). This FCE is a detailed test to see what your friend can do safely for 4 hours of work. We are all created differently so the hip shouldn't be the sole parameter of assessment.
I highly suggest you you them one at a time and space it by 3 months. The bilateral knee replacement triples your complication risk. If you do end up with a complication, you will look back and ask why.
Realistically 7 months later if she is still having significant swelling, there is likely an issue with stability, loosening or maybe infection. My recommendation is to go get a second opinion. You are right, there is not a normal presentation. Your doctor should be doing tests (blood work, x rays, bone scans) to rule out infection, loosening, etc.