Complex sentence: Mulholland left the cast of "Chicago" at the end of March 2007, however on 5 December 2007 she was, as a past Roxie, invited back to attend the 10 Year Charity Gala performance and Black Tie Reception to celebrate the production's tenth anniversary.
Split into simpler sentences: Mulholland left the cast of "Chicago" at the end of March 2007. On 5 December 2007, she was, as a past Roxie, invited back to attend the 10 Year Charity Gala performance and Black Tie Reception to celebrate the production's tenth anniversary.