Very little information is known about Anthea (not Antea; in Wrong Exposure, Aelita said the name with a 'th' sound.) Schaeffer.

In the events during The Key, she is a pink-haired woman, which explains where Aelita's pink hair came from.

After being kidnapped (as shown in Distant Memory) by men in black on their vacation to the ski lodge, Aelita and Franz Hopper move to The Hermitage and later virtualize themselves to Lyoko.

Her maiden name was Anthea Hopper. When Waldo Schaeffer (AKA Franz Hopper) changed his name, he took her maiden name. The Project Carthage folder also includes a photo of her skiing pregnant. This gives an idea of Project Carthage's length.

Anthea was believed to be kidnapped by the Men In Black before Franz Hopper created X.A.N.A. (we can deduce this by X.A.N.A.'s lack of ability to create a polymorphic clone of her for the simulation bubble in Distant Memory).