Lena is the niece of Magica De Spell, who forced to do her aunt's bidding. She has yet to make an appearance outside media associated with DuckTales .
Lena is an edgey, goth teenager and greatly admired by Webby. As mentioned above she is the neice of Magica. At first she seemed to be helping her aunt get to Scrooge's number one dime, by pretending to be friends with Webby, but it is revealed later that she actually has developed a fondness for her.
In the season one finale, the ducklings discovers that she was actually a shadow created by Magica to get revenge on Scrooge and free herself. During the final battle, Lena's able to strike back at Magica, but ends up sacrificing herself to protect Webby. Unbeknownst to everyone, however, she now exists as a manifestation of Webby's shadow due to the friendship bracelet the latter wears.