It’s true. She doesn’t know any other cases.
If you want to skip Biden’s answer to the question, go to around 2:03. I found his answer to be surprisingly good (politicians tend, at least in my opinion, to be pretty bad at giving the reasons for why certain cases are “bad” or “good”), even citing the trimester framework established in Blackmun’s opinion. That said, watch Palin to be truly frightened. Really. I’d laugh if I wasn’t so afraid that she could actually be veep.