Ernie - congrats on a great adventure ahead of you both.
Sounds like you both a well suited. Just wanted to share a few pointers of my experience, having walked the portuguese in May last year (4 weeks)
I would not second the notion that much of this route is flat and on board walks. that is not a correct reflection of the camino portuguese in my experience and would be misleading.
The only boardwalk I ever encountered was on the day out of Porto/Matasinho onto Vila de Conde. Yes, that was rather flat, as one could expect walking alongside that particular bit of atlantic ocean. - But Diogo posted a few days ago about new boardwalks installed in a section after Lisbon (happened last fall apparently) - he also posted a few photos. search this thread and you will find other good info too...
otherwise to add:
The only steady flat part was the area of the Tejo river area -
It gets hilly and steep in parts, but none would be like crossing the alps or such. I believe the hightest elevation change within one day was out of Ponte de Lima at sea/river level up to 430 meters or thereabouts. So, there was some huffing and puffing about for sure!
There is also much walking on tarmac and cobblestones and old roman pathways - hence, investing in good shoes is highly recommended for sure.
I never pushed myself for long days. Never saw the point of that. For me it was a good mix between 15km - 27 km days. First day though I started off w/ just 11km. - I wanted to end my walking days still with a smile on my face and energy enough to perhaps explore the sights... so i never rushed or had an agenda.
sounds you mum would be in good shape for that.
people have posted numerous photos on the caminho ... below a link to the images i've taken... enjoy...and bom caminho!
https://www.caminodesantiago.me/community/camino-photos/users/amorfati1.22497/