So we all know that even all the way back in the comics and the OG Ducktales, Magica was always after the dime to snag it as an ingredient to the Midas touch or in the 80s series case, a token to restore her brother back to normal.
In the reboot however, at least during her arc in S1, we learn that here she was after the dime because her physical form was trapped inside of it. However...
Fast forward to Life and Crimes and we learn of how her and Scrooge first met, turns out she was ALWAYS after the dime, even before she was trapped in it, so why would she be so attracted to the dime in the reboot that makes it so special? Even after she's released, she still wants possession of it as seen during the court trial.