In fact, she once shouted at an illusory and said he should be ashamed of himself in.
Amber tells Mewtwo not to cry and that there's a story that says Pokemon tears are full of life and that Mewtwo shouldn't be sad for her because he is alive and life is wonderful.
Near the end of the story, the climax gives off an intense feeling of empty sadness as a tragic battle drags our main character right in the crossfire, leading to an unfortunate event, of which I will not spoil.
In that context, her outfit and preferred Pokémon type start to make a lot of sense.