Personally I do love the idea of a superheroine who grows giant getting her powers scaled and amped up proportionally to her size.

But then I like the idea of giantesses having more abilities in general than just being big, like they have deified abilities that make humans fear and respect them as actual gods instead of just large bullies with a height advantage.
They could use this in a beneficial or harmful way, like a giantess who controls lightning offering to power a city for her humans in return for their love and loyalty, or just flinging lightning bolts with playful abandon and terrorizing them that way.