Hi everyone,
Alex you´v got plenty of good advice but as I am a lady of a "certain age"
I would like to tell you to get button shaped pearls for earrings for your mother. They look much better, right backsettings or not. I almost never use my round pearl earrings anymore, despite being Freshadama quality. Up to 8,5 mm round could be OK, larger - choose buttons. As for the likeness of freshwaters to South Sea - in this case it is about the size, as South Seas start off at 8 mm and then can be very huge depending on the nucleus inside the shell. Colourwise freshwater have of course a more satiny look than Akoyas but fine South Seas are even more "satiny" in their looks. And they are bead nucleated.
Take a look at "South Sea Pearls" thread The big strand by Airdancer from yeaterday and you can see the finest available of South Sea Pearls, I tried to copy the link but get the wrong "picture" all the time....
As for quality: very soon we are going to see Freshwater pearls with a nucleus inside (there already are some) and then they also will have joined the rank of all the other beadnucleated pearls with only some layers of nacre instead of nacre all through. Some member advised on the "City strand", a lovely choice in itself if your mother already has aquired some taste for pearls, otherwise this length is perhaps better suited for the "advanced wearer", I speak out of my own experience of course. Nowadays I have several Opera lengths and love them but at the start I was absolutely happy with a necklace of 18", size 8-8.5. For my agegroup I think 9-9,5 mm do look very great but again, in the beginning I did not believe that a little larger size would be so good looking. Give the seller a call and you will get personal advice - good luck and let us see and know on what you decide...