Change them back

Just as Supergirl gets over the shock, and begins to look happy with her new endowment, you decide to change her back.

"Make them small again." You say to your magical companion.

"Erotser stit!" Zatanna casts.

Supergirl's breasts begin to shrink in her hands. "No, wait!" She shouts at them in vane. They return to their normal size. "Aw man! I wish they were as big as Power Girl's permanently!" She shouts, looking up to the sky in hopes of some kind of a response. She goes back to looking at herself in the mirror. Looking even more unhappy with her her chest than she did before you interfered.