Did the student have other sources (especially ones that also address the topic in the SD article?) If it is her only source, then it isn’t enough and she should be marked down for it. If it was a starting point, or perhaps even referring only to one brief point she made, but the rest of her sources are satisfactory, then I think she should get full marks.
There is nothing wrong, IMHO, in using a source like the Straight Dope, or Wikipedia, or the World Book encyclopedias as long as they aren’t your only sources. I’m working on my second university degree, and when I have to write about something new, I always start with a general reference, to understand how to approach my topic and to figure out what key words I need to be researching for, and I have never been marked down for it (I do include it in my list of references).
ETA: I do, of course, do the rest of my research and cites from actual books/journals/etc.