For nineteen years, as Matthew Lewis relates here, England was torn between Matilda, Henry I’s only surviving legitimate child, and Stephen of Blois, his nephew. She married Geoffrey of Anjou before their son Henry II succeeded her rival, but her position was difficult because of her gender. The concept of a “Queen Regnant” was unknown at the time and she sought the title “Lady of the English”, as used by Ethelfleda of Mercia. There was some suspicion that Geoffrey sought to assume her authority.
Here is an edition of Melvyn Bragg’s excellent In Our Time, about Matilda’s contemporary Melisande, who was Queen of Jerusalem between 1131 and 1153. She was married to Fulk of Anjou, Geoffrey’s father and thus a male line ancestor of all Plantagenets, who really did assume much of Melisande’s authority, which is why some nations had a Salic Law, precluding female monarchs and inheritance through the female line.