Seiya said:
To be fair Usagi can reliably be either green, indigo or a star sapphire. She runs on Love & Hope equally and she had enough will power to bring everyone back to life and keep her body/mind/soul in tact while her universe was trying to erase her from existence at the same time.
Given her "acceptance" of Chaos as a natural part of reality in at least one continuity she might very well qualify for White Lantern.
Usagi does have experience with the more "negative" traits of the rest of the spectrum.
She can be greedy(dear lord that girl loves her food), she has had inconceivable rage at times(don't even think of saying she did not face this when confronted with the actions of the more horrific villains, no sane being would not) she just refused to ever give in to it, and most importantly she knows fear quite well considering all she has faced in the past.
It's just that these parts of her are relatively small compared to her unyielding courage, endless compassion, all encompassing love, and boundless wellspring of hope.