Angel Ashley isn't complaining, mind you. Not really. She just gets bored sometimes?
Like, the most evil Devil Ashley tends to get is pushing for doing something she thinks someone else will appreciate, but for SELFISH REASONS! GASP!
Ashley's actual height is the middle between Devil Ashley's height and Angel Ashley's height. I originally imagined an overall size difference with the angel being a giant, but wound up wanting to draw Angel Ashley holding Devil Ashley back in their first appearance, so it became a height difference.
And possibly some other differences, but those are undoubtedly too subtle to notice.