Summer Glau was 28 in Superman/Batman: Apocalypse when she played the character 'Kara Zor-El / Supergirl (voice)'.
That was over 14 years ago in 2010.
Today she is 42, and has starred in 13 movies in total, 6 of those since Superman/Batman: Apocalypse was released.
In Superman/Batman: Apocalypse, I think Summer Glau looks: