Euphie's life consists of everyday brutal torture and rape, and she lives in Room 101. She still believes the Power of Love will always be there to comfort her.
Justified: Euphie is The Cutie and the Moe girl, or just a child. What do you expect?
She has lived a very sheltered life.
Euphie is The Messiah and believes that by treating others with respect it might, eventually, be returned.
Euphie does her hardest to live up to the ideals she has, but the cruel reality and all of the torture done by those manipulative and ungrateful bastards makes it very hard for her. She becomes more and more cynical and disillusioned as time goes until she finally lose all of her idealism, regrets her idealism and reacts to it... by destroying/regretting everything she has worked for and resigning oneself in constant wangst.
Euphie becomes a Well-Intentioned Extremist to force the world into becoming a nicer place, and you know what, The Extremist Was Right. She happily discards her hardened mindset to enjoy the world she's created.
Her allies were fighting over her because they were all in love with her and fighting is how they've always gotten things done.. The fact that they defeated the Big Bad with (loving) violence reinforces this idea. Euphie decides to Marry Them All with herself as The High Queen.
Alternately: her idealism is shown to be laughable half the time, but the other half the time she is right on the money when it comes to believing in people.
Averted: Euphie's idealism approximately matches that of the world around her.