It's not often an actress can play a character, then play the character's aunt 24 years later.
Helen was the first actress to play Supergirl / Kara Zor-El in any medium in Supergirl: the Movie (1984)!
In 2008, she played Kara's aunt, Lara-El (birth mother of Kal-El / Clark Kent), in two episodes of Smallville! (She also appears in a documentary on the Season 7 Smallville DVD set entitled "Supergirl: Last Daughter of Krypton")
And she still looks...well...SUPER!
Currently a regular on the new TeenNick series Gigantic as Jennifer Moore.

Other actresses to play Supergirl / Kara Zor-El / Linda Lee Danvers since Helen include
Nicolle Tom (Superman: the Animated Series, New Batman Adventures, Justice League Unlimited)
Laura Vandervoort (Smallville)
Tara Strong (Justice League Heroes video game)

Other actresses to play Lara-El aka Lara Lor-Van before Helen include...
Agnes Moorehead (Adventures of Superman [radio] "The Baby from Krypton" [1940], "Superman Comes to Earth" [1942])
Luana Walters (Superman[1948 movie serial] "Chapter 1: Superman Comes to Earth")
Aline Towne (Adventures of Superman "Superman on Earth")
Susannah York (Superman the Movie, Superman II, Superman IV: the Quest for Peace)
Britt Ekland (Adventures of Superboy "Escape to Earth" and "Abandon Earth")
Eliza Roberts (Lois & Clark: the New Adventures of Superman "Foundling")
Finola Hughes (Superman: the Animated Series "The Last Son of Krypton")
and, Kendall Cross on an earlier episode of Smallville ("Memoria")

Other actresses to play Talia al Ghul include...
Olivia Hussey (Superman: the Animated Series and Batman Beyond)
Andrea Bowen (Batman: the Brave and the Bold)

Best known for portraying famous real-life women, including Tina Turner, Dr. Betty Shabazz (in two films; Malcolm X and Panther), and Rosa Parks, Angela's roles have primarily been strong, assertive characters who dominate the situation in films like Waiting to Exhale and How Stella Got Her Groove Back, not unlike her current role: Checkmate's leader Amanda Waller in the new Green Lantern film!
Trivia: Angela's the only actor to play opposite live-action versions of both the Silver Age Green Lantern and The Flash!
Other actresses to play Amanda Waller include...
Pam Grier on Smallville
CCH Pounder on Justice League Unlimited and Batman Beyond as well as Superman / Batman: Public Enemies, which is set in a different continuity.