How? None of the female characters did anything in that show, except Wang, who magically accomplished everything.
This episode definately showed C.C. is a strong character, after everything she has been through, shot, tortured, betrayed, never finding true love, she didn't take the easy way out and just died, she chose to live on, granted Lelouch was a major part in that, but still.
The memory loss I'm thinking is temporary, I think Lelouch most likely has to grant her wish for her to gain the memories back, or at least that's how I'd like it to go.
Kallen just hasn't had her moment yet, she has had a decent battle here and there, but her time just hasn't come yet, other things have taken priority for the most part.
Nunally is a rather strong character, this episode proved just that with her standing up to those around her telling her what to do.
Cornelia is awesome, like you stated.
Though Shirley was indeed ditzy and silly, I think it says a lot for her character that she was able to forgive Lelouch in the end, despite all of the pain he caused her, she was able to look past it and realize he was a good person, unlike other characters.
Even Euphemia wasn't 'weak', throughout all of her life she was always put down as the one who knew nothing about war and was simply there to be the Princess that got everything, something she didn't want, but when her moments came she was shown to be a compassionate female who wasn't even racist like the rest of her family. While Lelouch messed that up, she still had her moments.
Compared to 00, I believe Geass has far stronger females. You are just looking at all of fanservice and counting that against them far to much, they have done a lot of good also.
Edit: And majority of the people in this thread I have seen in the 00 discussion thread, so I don't think anyone is being spoiled all that much.