“Best” Last 100 km route for me and my mom?

I’d walk from Valença/Tui. Fly into Porto. Quick train ride to Valença. Great old town for lunch/drinks before the short walk to Tui. Start your Camino the next morning. You’ll have a couple towns with alternative, slightly longer routes into town. Take the alternate along the river every time. It’s much more pleasant.

And consider staying in Milladoiro the night before Santiago. It’s at the top of a long hill. The albergue is new (so is the city). The next morning you’ll have an easy 8km saunter to the Cathedral in Santiago. Otherwise the final day is a 28km slog with a mid to late afternoon (aka the hottest part of the day) arrival at the Cathedral.

Buen Camino!