If you are looking for a weekend walk on the SW Coast Path without too much scrambling or climbing, but hopefully taking in some typical sections, how about a walk on the Lizard Peninsula, from Coverack to Helford Passage. This is about 15 miles total, with a possible overnight B&B stop at Porthallow (the half-way point on the SWCP). You get plenty of cliffs, possibly a chough or two, peace and quiet, two estuaries, a short ferry crossing and continuous beautiful views. And there are a few refreshment stops on the way. If you want to do this as a one-way walk then Coverack can be reached by bus from Helston, and Helford Passage could be reached by bus from Falmouth. Just one of very many possibilities.
Whatever you choose, I'm sure your mum will enjoy the SWCP experience.