Really the story is like that, Equestria was a safe place, there was a strong friendship, but by Lady Owl, made everything change, she wants to destroy the magic of friendship, but first, she has to destroy the princess of friendship, it is impossible to defeat Lady Owl, nor the magic of friendship can defeat her, That’s why Twilight is preparing her daughter to be the next princess, but she really doesn’t want to, because she doesn’t know what true friendship is, the only thing she wants is to be free, her dream is to save equestria, her family and friends, she’s not ready to be a princess.
 
||||

she didn’t say a soldier. she said a warrior.

If you want to save Equestria, being a princess is a far better way to do it.
 
Battles are best won by strategic planning making them happen on your terms, and by the preparation in the days, weeks and months leading up to them.
 
Wars are best won by long-term planning making them happen on your terms, and by the preparation in the years, decades and centuries leading up to them.
 
And individual soldiers can’t even effect the preparation for a battle, but play one small part.
 
But an alicorn princess can set policy and steer culture for the centuries before a conflict, and even, by being in a position of power, avoid conflicts altogether.

Trust me, you’ll have to do both eventually.