You are right about that backstory. Tinkerbell found Regina's true love and Tink told her where he was - at a local tavern/inn. Regina looked in the window, saw him [Robin Hood], started to open the door, then stopped and left. Taking the time to help Regina caused Tinkerbell to be late coming 'home' and the Blue Fairy was waiting for her. For disobeying, Tinkerbell was stripped of her pixie dust. In essence, Regina failing to follow through with true love caused Tinkerbell's downfall.
Never thought I would type out a paragraph like that with a straight face.