depending on where she lived, it might have been a long time getting to the muslin, or maybe she was trying to figure out a way to NOT have to sew in two diamonds. Or, there was an unexpected move, or life just got in the way of finishing the project. And, as you said ... setting in the diamonds were a challenge, though not as much a challenge by hand as by machine.
The fact that she held on to those blocks at all is a miracle.
And, to have continuing generations save them for a quilter that they weren't even sure would appear in their family ... that is a real gift!