I actually watched this episode for the first time (I hated the synopsis) and when I saw the flashback, all I saw was Kuvira seeking to share her views and way of life with others, not even a desire to help others first. I thought at least the flashback would show her original goodness and altruism but all I saw was a well meaning but misguided desire to push her ideaology on others.
Actually I'm starting to believe Kuvira always wanted greatness. She was certainly not bad at her youth, but she certainly always wanted more. She was the captain in Book 3, she certainly was not a nobody. I also get the impression that having that huge amount of power untapped some sort of inner desire that has lead her to seek more an more land and with it more power.
"Nearly all men can stand adversity, but if you want to test a man’s character, give him power"