I hardly think it's appropriate to apply modern day labels to historical figures. You're saying, "No, I don't know how she would have identified, but we're going to use her in our discussions as bi/pan, anyway." That's blatantly disrespectful. If you want to say that Anne Frank was interested in girls, that's one thing. It's a fact. But slapping 2014 queer politics onto a victim of the Holocaust? Please don't.
I’m just saying that she explicitly expressed interest in multiple genders, which fits our definitions.
And if we’re talking about the historical habit of erasing non-heterosexual identities, especially that of multisexuals, then it becomes relevant that Anne Frank has been presented as straight within her abridged diary for decades. (And we can talk about how deeply disrespectful it is to even present an ABRIDGED diary of someone without their consent for what does and doesn’t get abridged.)