Saw this on MSN news. Definitely a scary thing to happen.
Looks to me that she was tailgating just a little...(can't even count 1/1000, 1 second, between em)
And if I didn't know any better, I'd say that the truck she was following a little closely, intentionally hit the board. However, it's kinda obvious that he was just giving the bigger truck passing on his right some room, or was a little scared of it (which is likely). Since he's hauling a trailer, it's not like he can hit his brakes and/or jink to avoid it.
All in all, had she not been following THAT closely, it's VERY likely that she wouldn't have had that happen to her. One lucky lady.