Ellie and The Invisibility Spell!

Ellie, a somewhat short and skinny girl with short black hair and blue eyes, had a botched invisibility spell cast on her!

Now she's turning invisible at random, and worse, her clothes are vanishing when she does!

The time it lasts is unpredictable; she could be exposed again in under a minute or it could last all day!

Certainly this leads to a ton of naked embarrassment for poor Ellie!

How does it all happen?