If I read Franklin's notes this establishes that she did in fact conceive of a double helix and base complementarity in the center (I can't see if she also recognized it was antiparallel).

That's the first actual evidence I've seen (I am a DNA nerd and have been trying to understand what her contribution to the intellectual discovery of DNA's double-helix antiparalel).

I would need to go back to Judson's book (Eighth Day of Creation) and see if he actually missed this.

I happen to be reading Judson right now. Quoting from it here:

> It is easy to feel great sympathy with Franklin. The fact remains that she never made the inductive leap... before she learned about the model proposed by Watson and Crick, she and Gosling began to draft a paper to state their conclusions so far about the B structure. That draft also survived among Franklin’s papers. It was vigorous, clear, and limited. Klug and I went over it one afternoon in his office. “You see, she was lacking one final step,” Klug said. “Well, two steps. What she missed was the presence of the dyad—the symmetry of the molecule. Which Francis had seen immediately from her information about the space group. And even though her notes earlier showed that she knew about Chargaff’s ratios, she never got to the base pairing.”

Seems like Judson accepts Klug's version of the story: she understood that the structure was helical, but not that it was doubled or base-pair. There's also a final essay at the end of the book "In defence of Rosalind Franklin" which basically reiterates this:

"She had not perceived that the backbones run in opposite directions. She had not started modelling the B form as a double helix and so had yet even to encounter the problem of fitting the bases inside."

I'm a bit confused about this discussion about whether or not she conceived of a double helix structure as this PBS Nova documentary on DNA includes a scene where they show her notes that have her muse about the possibility of a double or triple helix structure.[0]

As for base complementarity it seems likely that she would have made that leap from everything else that she knew of at the time, but I'm no expert on this subject and have not read her notes.

[0] https://youtu.be/_1FUqUSNPeI?t=2487

where did she say she knew it was a double helix?

FTA:

The new paper does not challenge Watson and Crick’s achievement. Their model of DNA, rushed out in a brief article in Nature after Watson caught his glimpse of photograph 51, went well beyond Franklin’s understanding. [Watson and Crick's model's] two strands running in opposite directions and zipperlike arrangement of complementary base pairs explained how the molecule could carry genetic information and be copied each time a cell divides. “The fact that it was a helix, you know, was not the most exciting aspect of this structure,” says Soraya de Chadarevian, a science historian at the University of California, Los Angeles. Indeed, by 1952, other researchers striving to make sense of the molecule also suspected it was helical. [for example Pauling, who at one point thought DNA might be an alpha helix-like structure]