I think that's just the author just being inconsistent with the sizes. It's not the first (and definitely not the last) time they've had some size inconsistency.page 10, I know Mine grew, but how come Giraffe looks so much bigger, too? (even tho he's getting squashed)
This would've been a very good prediction if this manga had logical consistency.I feel like her power miiight be psycho-somatic. Like, she gets bigger if she FEELS like everyone's attention is on her.