Selina actually *worked* with Oracle, indirectly and reluctantly, twice, at least one of which came before this. Which is why Huntress is there; they'd had two team-ups at that point, one of which was the second (or third? the publish order isn't the same as the story order on the early BoP minis, so I always lose track) mission Dinah ever did for Babs. Selina, Helena and Dinah all dated the same con artist and teamed up for revenge, and Selina was aware of Dinah's partner.
She'd have, however, no reason to associate that partner with herself or Bruce, or any concept of said partner's face, age, or even race or gender, with which to construct a visual for her fantasy.
Bruce eventually presumably hooks them up properly, as they do have occasional contact much, much later in their careers, and Helena gets her to help with the Babs jailbreak, but she probably *still* didn't know who Babs actually *was* (beyond, perhaps, "former Batgirl") until the four-page rolodex spread during the Spy Smasher arc, when Dinah has a bunch of her friends and a handful of Barbara's show up to intimidate Katarina. At which point everybody and their mother could find out her whole life story by checking the building ownership. But this is years before that.