Oh my! Good luck to you and your friend. I have no experience with wheelchairs on the Coastal Route, but I DO have experience on the Central Route. We met up with a young woman in a wheelchair a day out of Porto, in Vilarinho. We stayed with her for many days, and it took a
team of men to get her through. Often she would just map out her own route along the highways, but several times we took turns pushing/pulling her through sections that she would not have chosen, had we not volunteered to bring her with us. You can read our story, starting on
our day sixteen. I think the info will be useful. She was able to do very short distance walking, so she could stay anywhere, fortunately.
I have also walked the Coastal/Senda Litoral, but without a wheelchair person. There are lots of boardwalks to make it easier, albeit a bit rattly. You can see the many photos,
starting here to get an idea of each of our day's journey and what the terrain looked like. I particularly recall on our
day twenty, having to climb up and over a mountain pass, but that could be avoided by continuing on the road to Baiona. Oops, I see you are starting in Baiona so that won't matter!
You would have to look at each day's route and determine what would be best, based on how much you had to assist the person in the chair. We also found that many, many fellow pilgrims were willing to help push our friend if/when we got in a jam!
Good luck to you and buen camino! ~ Elle