Clickbait headline which misframes the controversy, to nobody's benefit.

Helical DNA was the strongest candidate by 51, in part because earlier and cruder X-ray diffraction images had existed for some time (10+ years) and were suggestive of this structure. All of the scientists in question, and many others, collaborated on that possibility at that time, and long before 'Photo 51'. It was not a surprise, but rather the focus of their work.

Franklin was making the famous improved images with the explicit intent of revealing or disproving the helical structure. She and her lab produced the most definitive evidence for helical B-DNA (Photo 51) in early 52, but during 52 the conclusion was still a matter of debate (and humor) amongst them - in particular Franklin was not convinced that A-DNA was helical. From Wiki:

> In July 1952, as a practical joke on Wilkins (who frequently expressed his view that both forms of DNA were helical), Franklin and Gosling produced a funeral notice regretting the 'death' of helical A-DNA

This left the molecular structure and number of strands as open questions. Triple helix models had been attempted by Pauling, Watson and Crick at that time. Watson and Crick though were first to develop the successful double helix model with antiparallel base pairs in early 1953. It is likely that Franklin had also come to the conclusion that DNA was a double helix by this time (based on her draft notes + circumstantial evidence) but she did not do so in total isolation, nor did she complete the final molecular part of the puzzle (though she had worked on it).

TL;DR DNA structure was not a eureka moment spurred by a single breakthrough thought or piece of evidence; many scientists collaborated on eliminating various likely possibilities for years until the correct model was found.