Three tries later, I have successfully cast off the center triangle of my mother's shawl. I couldn't get it loose enough with the needles I knit with, so I went up two sizes and cast off loosely, and I'm now happy with how it looks.
And a second picture for a marginally more accurate color:
Next on the agenda: picking up stitches for the (very wide) border. Hopefully tonight.
This weekend I managed to pick up the stitches for the border of the First Year Shawl, and knit the setup row. Now I'm once again stuck contemplating border options. I'm thinking of using the edging from Stephanie's Snowdrop shawl (PDF). No pictures yet, cause currently it's boring.