Good idea, thanks!

It's interesting, I speculated that the earliest break point in terms of writing style on the Crimebuster strip that I could see was Boy Comics #30, and here that's the first issue they have her credited with, though it's for the backup strip Swoop Storm. I also see that she seemed to be the main writer on the Sniffer strip over on Daredevil, and it's speculated here that he was writing the Sniffer and Iron Jaw strip in Boy Comics at the end (#110-119). Sniffer moved over from Daredevil around Boy Comics #80, though, which makes me wonder if she was writing the series the whole time. If so, it's another possible jumping on point, as when he moved over it started with a three issue appearance in the Crimebuster strip. It might make sense if she were writing both. 

I'm not convinced she wrote the Crimebuster strip thugh, only because Biro was notoriously proprietary about the character, to the point where he insisted drawing Crimebuster's head for every cover - other artists would draw the cover, and then Biro would paste on a head for CB that he had drawn, much like the corrections to Kirby's Superman. I think it's possible that Biro continued to write the Crimebuster strip throughout and just farmed out the backups. But I'm not sure. If Hubbell had taken over the book around #80 on the strength of her Sniffer series, it might also explain why Crimebuster lost the lead and cover spot for 15 issues or so during this time, replaced by Sniffer and Iron Jaw. 

Hmm...

I'm not quite sure either, but I do know that Stan Lee held Biro in high regard and in some ways patterned himself after Biro. It wouldn't surprise me if there was some form of the Marvel method being used during the 50's when Biro's plate was much fuller, with him maybe just giving basic ideas to his writers - or possibly, as you say, scripting over his plots.