So, it might be interesting for the discussion to note that before Isabella took the throne in 1474, the only woman to rule Castile was a Queen Berengaria for a few months in the thirteenth century, who abdicated as quickly as possible.
Point being that women could and did become queens regnant in countries where there was not previously any extensive tradition of female sovereigns. Of course Isabella did then co-rule with Ferdinand, but in this she was anything but a puppet.
Actually there were a few female rulers during the Bosworth era in addition to Isabella of Castille. The Regent of France was the King's twenty something older sister, Anne Beaujeu and Burgundy's sovereign Duchess had been Mary of Burgundy.
Yes, England was a different country and had issues with women in power before i.e. Empress Matilda, Isabella of France, and Margaret of Anjou, but to Elizabeth's advantage she was an English borne princess and a daughter of a very powerful man. And post-Bosworth there aren't so many candidates with good blood claims to the throne. I would count her and Warwick and perhaps Buckingham (depending on his age). I wouldn't include Lincoln.