Thank you so much for your help.
I find that the media refresh icon does not change things.
Running "sginfo -l" as user does not produce any output. When run as root, vl-hot promptly displays the icons on the desktop.
Is there a way of having sginfo -l do its job, without the root password? (I would prefer not to give it to my girlfriend, given that she knows hardly anything about linux)
As a solution, I added mount /dev/sdb in /etc/fstab. In this way, the sd card shows up in the mounter applet in xfce. Clicking it does not mount it by itself (the device is actually sdb1), but triggers vl-hot and the icons show up on the desktop. This way, mounting the sd card is a two-step process, kind of halfway between mounting cd's and mounting usb pendrives.