Since I hadn't read Snopes' take on the matter, I followed TBogg's link, and came across this paragraph from the report on the incident issued by the Federal Air Marshals service:
The source said the air marshals on the flight were partially concerned Jacobsen’s actions could have been an effort by terrorists or attackers to create a disturbance on the plane to force the agents to identify themselves.
This makes a lot of sense. No one has ever said the terrorists are stupid (misguided, maybe; animals, yes; but stupid, no).
I think if I were planning to highjack a plane [note to TSA: I'm making a supposition here, not a confession; I'm not OJ Simpson], it would probably be nice to know if there were Air Marshals on my flight, and if so, who and where they were. Since one can't very well stand up in the middle of the flight and ask the marshals to identify themselves, having a sympathetic (to the cause) yet obviously Anglo woman start trouble would be one way to get the info I want.
And Anglos do sympathize with al-Qaeda and the rest of their ilk... for instance, (left to right, above) John Walker Lindh, Richard Reid and Jose Padilla (okay, Padilla isn't Anglo, he's Hispanic, but you know what I mean). None looks particularly "Muslim", yet all were "fighters for the cause", at least in their own minds. So it wouldn't be impossible for al-Qaeda to recruit a non-Arabic-appearing woman for the purpose.
A propos of nothing, while I was searching for the picture of Lindh, I ran across an outfit called FrontPageMag (no link, cause they seem to be even more rabid than Malkin); Lindh's picture was in an article entitled "The Ten Most Dishonorable Americans"; in addition to Lindh (who certainly is dishonorable), the list includes Michael Moore, Danny Glover, Oliver Stone, and US Reps James McDermott (D-WA) and Barbara Lee (D-CA). As I say, more rabid than Malkin.