From the Fire Emblem Wiki:

Eirika is a merciful soul that detests violence, she is a forgiving and gentle person that suddenly needs to lead an army. She wishes that there was a way to solve their issues without bloodshed, but accepts that in the times of war, battling is a necessity for stopping conflict and bringing peace. She is innocent and very naive due to her sheltered childhood, being it her worst flaw. That aside, she adapts quickly to the circustances, and matures while learning the effects of the war. She is a quick thinker and level headed, being very educated with knowldgement on geography and history, also having developed diplomatic skills.