Fleance, along with Banquo (whom she once dated), assisted Macbeth in at least two of his activities: stealing the Scrolls of Merlin, and aiding him on his quest for Excalibur. ("A Lighthouse in the Sea of Time", "Pendragon")  They also were present at his wedding to Dominique Destine in Paris. ("Sanctuary") Fleance and Banquo are aware of Macbeth's true identity as the Macbeth.
Later on, Fleance and Banquo left Macbeth's service, and went to work for Castaway (an ironic choice, in view of Castaway's descent from Duncan and Canmore). They helped him set up the Quarrymen and train his recruits, and fought Goliath and Elisa alongside him. ("Nightwatch", "The Journey")
Fleance is a human woman. She is muscular and somewhat acrobatic. She is capable of flying various aircraft. In the outline memo for "A Lighthouse in the Sea of Time", Greg Weisman muses that Fleance is not her true name, and that Macbeth only insists on calling her Fleance as an inside joke that she might not fully appreciate or understand. 
- "A Lighthouse in the Sea of Time" (First Appearance)
- "Sanctuary" (No Lines)
- "The Journey"
- "The Rock" (Indirect Reference Only)
Real World Background
Fleance is never actually named in the series, but only in the ending credits. Her name comes from Fleance, the fictional son of Banquo in Shakespeare's play Macbeth, who escapes his father's murder by Macbeth's henchmen and eventually becomes the ancestor of the Stuarts.
Voice Actor: BJ Ward