Being well hydrated is good general advice, but shin splints are an impact/overuse injury of the tibia and associated tendons, and it is the causes of these that need to be addressed to prevent or treat the condition.
Prevention: gradually build up to the distances one is going to walk, which for the OP might not be something she can do in the next three days, but would otherwise be the easiest way to avoid any overuse injury. Before you leave, replace your footwear insoles with a good, shock absorbing insole. When on the Camino, warm up and stretch before doing serious walking. This might just mean taking it easy for the first couple of km. Avoid walking on hard surfaces if you can, although this is not as easy as it sounds.
Treatment: if you do get shin splints, my view is that relative rest is the first thing to do - slow down, and don't try and keep walking through the pain. Stop if you have to and rest, but if you do, remember the other elements of RICE - ice, compression, elevation. When you can apply ice if it is available. Also consider taking an anti-inflammatory such as ibuprofen or using an NSAID cream such as Voltaren. Apply a compression bandage and elevate you legs. Its a great excuse for sitting around with your legs up!
I know it is in the nature of the pilgrimage to push on, but if the condition persists, seek medical advice at a farmicia or medical centre rather than keep walking in pain.
Regards,