Who is Fraulein Nadia Vole from Stormbreaker and what is their importance?

Fraulein Vole is an employee of Mr. Sayle's. Vole escorts Alex to the Stormbreaker each day and she is the one who catches Alex when he finds the basement door that leads to the secret lab. Vole tricks Alex late in the book, convincing him that she had been working with Ian Rider, but then she causes Alex to fall into the aquarium with the jellyfish when she pulls the arm of a statue that opens a slide into the aquarium. Vole is killed when Alex melts the metal of the aquarium with a special cream made for him by MI6 and the jellyfish is released on top of her.