1956: Batwoman makes her first appearance in Detective #233 (July).I was focused on what was happening in the culture that would cause this sudden interest in female characters and I missed what was right in front of me all the time:
1957: June Robbins makes her first appearance with the Challengers of the Unknown in Showcase #7 (March-April) Lois Lane makes her solo debut in Showcase #9 (July-August) Queen Arrow makes her only appearance in Adventure #241 (October).
1958: Lois Lane gets her own title (March). Supergirl tryout in Superman #123 (August).
1959: First Lady Blackhawk appearance in Blackhawk #133 (February). Supergirl (Kara) launched in Action Comics #252 (May). First Mademoiselle Marie in Star Spangled War Stories #84 (August). First Aquagirl (Lisa Morel) appearance in Adventure #266 (November).
1960: First Miss Arrowette (Bonnie King) in World's Finest #113 (November).
1961: Batgirl (Betty Kane) debuts in Batman #139 (April).
1958: Lois Lane gets her own title (March).
We don't have circulation numbers for any comics before 1960, but I suspect Lois Lane sold like hotcakes right from her first Showcase appearance. By 1960 her mag was the #11 selling title in all of comics, moving 458,000 copies per issue. So of course the DC editors realized that there was a market to be tapped, and they rushed to try to fill it.