Radigund, the Amazon queen and warrior-princess, is pretty much a foil to Britomart, another female knight. But while Britomart embodies chastity and never tries to claim power over men, Radigund uses her physical strength and position to subject men while also secretly lusting after them.
This is exactly what happens to Artegall, who is captured by Radigund and then she develops a big crush on him. It's fitting that it's Artegall who must deal with Radigund since his one true love is Britomart, so he must face her opposite in order to truly understand what makes her special and unique. Of course, Spenser had to handle Radigund very carefully, because with Queen Elizabeth in charge of England, he couldn't condemn too much the rule of women over men.
So he goes to great pains to present Radigund as also a poor ruler and a cruel tyrant, one who doesn't just command men, but enslaves and emasculates them. Britomart, on the other hand, liberates them and (eventually) increases their manly self-confidence. Thus, Radigund represents female power gone wrong, while Britomart represents it properly deployed.