The Blue Fairy was called the original power, not ultimate bad nor good. Right side means neither good nor bad side, it is a matter of perception. She has helped everyone she’s encountered so far whether they liked what the result was or not the choice was the right one good or bad. She does have an ulterior motive yes but again it will be for the right side; good or bad. There was nothing sneaky about her and if sneaky means not trusting Rumple/ Gold then yes she is sneaky because he is a snake and cannot be trusted unless you have a deal with him.
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