FoxHawke said: More like make Estelle's boobs bigger.
I thought Rita believed larger breasts "just got in the way," so maybe in this picture's backstory she tried casting a "cup-size reduction" spell so that Estelle would see things Rita's way ("Don't you feel so free without those wagging around your chest?").
The way I think of it, Rita wasn't specific enough as to what the final result of "Make Estelle's cup size smaller" was, so instead of just doing that, it also reversed Estelle's age to when she was as flat as a board.