Okay, I guess.
@Oddball64
She was italian, lived next to mount Vesuvious and made a living selling (genuine) magic potions to whoever could afford them.
The reason she wanted Scrooge’s first dime is because on her introductory story she was buying coins belonging to rich people to use them as components for a magic amulet that was supposed to grant her the power to turn anything she touched into gold. Scrooge just sells her some pocket change and dismiss her as a loon, but then he notices that he accidentally included his first dime among the other coins, so he runs after Magica to get it back.
Magica realizes out that since that coin in particular has been with the world’s richest man for decades, it’s the world’s most powerful magic component for her amulet and refuses to give it back, since Scrooge freely sold it to her and so, it genuinely belongs to her. Scrooge takes the coin back by force, and that’s the origin of Magica’s crazy grudge against McDuck.
Magica CAN create her amulet using normal coins, but Scrooge made it personal and that’s why she’s decided to get Scrooge’s number one dime and make the old guy’s life as miserable as possible whenever she can.