While feeling mysteriously responsible for Medusa, Wonder Woman ranks herself pretty highly; she says "I know of only two, perhaps three, people who could face [the Hydra]," and then says "I can defeat the Hydra."
So, the Hydra can be faced by Wonder Woman, Superman (I'm guessing), or "perhaps"...Martian Manhunter? Shazam (if this is happening after JL 17 or 18)? Zatanna or some other top magician?
I'm guessing she meant she knew 2 or 3 besides herself, So I'd say Superman and GL are the main 2 (she was wishing she had their powers in the fight) and the I'm guessing the maybe is J'onn (who was able to hold off the whole JL at least briefly). I don't believe she has met the others in the same power class (Supergirl, Power Girl, Captain Marvel/Shazam) at this point. Has she met Heracles in her book? I don't recall him showing up.
Pull List; seems to be too long to fit in my sig...