Tolkien- For the Love of Eowyn!

[symestreem]

A cage... To stay behind bars, until use and old age accept them...

If you put something in a cage, it withers and dies. And why let Eowyn go in Eomer's place, except that she had not been trained to fight? And why was this? Because she was female. So genetic chance forced her responsibility on her.
And if Eowyn's 'redemption', so to speak, occurred at Minas Tirith, then the survival of her spirit (not soul) required her to ride, to break out. In exersizing her right to fight, she was fulfilling her responsibility to her people as well. What good is there for a ruler if there is no country?