You raise an interesting question of speculation, which I myself have. And you raise the same point about female succession in history: regardless of the particular laws (which have traditionally evolved out of default and circumstance, as opposed to being written in stone to reflect some *principle*), a queen regnant has not been possible in the presence of male agnates.

Consider how Stephen of Blois -- who was not even an agnate -- was able to usurp the English throne, despite it having been the right of Holy Roman Empress Matilda (the only surviving legitimate child of King Henry I) upon the death of her father. As it was, the most she could do was to secure it for her own son, who eventually ascended as King Henry II. It's anybody's guess as to what would have happened if she had only daughters, while Stephen had multiple sons ...

I've always maintained that if Edmund Tudor had lived AND fathered sons, the eldest would likely have been married off to the future Queen Mary I -- possibly as a joint sovereign. It's conceivable that King Henry VIII would have arranged a cousin marriage between his daughter and his hypothetical nephew (let's call him Henry).

This has actually been a common scenario in the Iberian peninsula: marriages between agnates, in part to avert a succession dispute -- despite the law nominally being male-preference primogeniture. Queen Mary I of Portugal married her own uncle, who became King Pedro III. Queen Isabel II of Spain married a first cousin, Infante Francisco. Unfortunately, it was the wrong cousin ... There might not have been a civil war, had she married instead her uncle Carlos or his eldest son ...