Allen is best known for her recurring role as the witch Amy Madison on the television series Buffy the Vampire Slayer.

[citation needed] Since 1992, Allen has worked regularly, primarily in guest or recurring roles on various television series, including Doogie Howser, M.D.

Her film credits have included roles in Timemaster (1995), Illegal in Blue (1995), and the controversial Silent Lies (1996).

Allen won the recurring role of Amy Madison on Buffy the Vampire Slayer for the season one episode "Witch".

She returned for a three-episode guest arc in the season six episodes "Smashed", "Wrecked", and "Doublemeat Palace".