Keegan studied at the Central School of Speech and Drama. Theatre includes: Susan in Abigails Party directed by Sarah Esdaile , ATG Tour, Alan Ayckbourn's The Revengers Comedies. A Message for the Broken Hearted by Gregory Motton, directed by Ramin Gray at The Liverpool Playhouse, Cunigonde in Candide, directed by David Farr at The Gate Theatre. Bedroom Farce, directed by Loveday Ingram at The Aldwych Theatre. The Ghost Is Here, directed by Kazuoshi Kushida, New National Theatre, Tokyo. Hushabye Mountain by Jonathan Harvey directed by Paul Miller at The Hampstead Theatre. She was picked by Kazuoshi Kushida to join his company at The New National Theatre in Tokyo and perform and sing in Japanese. On the film scene she played Transom in Thunderbirds (2004). She featured in Harry Potter and the Deathly Hallows: Part 1 (2010) as the red-haired witch and had a part in Driving Lessons (2006) with Rupert Grint and Julie Walters. Keegan has appeared in numerous British television programmes in a career spanning three decades. She made recurring appearances in Under the Hammer (1993) with Richard Wilson and was a regular on Hearts and Bones (2000) as well as making an appearance in Gimme Gimme Gimme (1999) by writer Jonathan Harvey.