According to the movie's commentary, she was originally at the audition to help out by reading against the male actors, but the director Gregg Bishop decided to cast her in the leading role after hearing her perform the lines.

[6] Alexander's next role was in the movie Squirrel Trap where she played Sara, the love interest of the main character, David, who is a socially introverted genius portrayed by Keith Staley.

This was soon followed by a guest appearance in It's Always Sunny in Philadelphia, where she portrayed a femme fatale in the role of Tammy, who through a combination of seduction and threats manipulates one of the main characters.

In Hallowed Ground she played Elizabeth Chambers, a girl stranded in a small town inhabited by a sect that plans to use her as a vessel for the rebirth of their founder.

In September 2009, Alexander was cast as Lady Sif in the live-action superhero film, Thor, directed by Kenneth Branagh and released in May 2011.

In July 2010, Alexander was cast in the independent comedy-drama film, Loosies co-starring Peter Facinelli and directed by Michael Corrente.

[10] Alexander appeared in the 2013 film Savannah directed by Annette Haywood-Carter, about Ward Allen (Jim Caviezel), a real-life early 1900s aristocrat who starts an unexpected partnership with Christmas Moultrie (Chiwetel Ejiofor), a freed slave.

[23] Also in 2012, Alexander suffered severe injuries when she slipped off a metal staircase during a rainy morning on the Thor: The Dark World set.

The fall caused her to slip a disc in her thoracic spine and chip 11 of her vertebrae, as well as dislocate her left shoulder and tear a rhomboid on her right side.