Magnolia was the fiancee of Colonel Beauregard. She lived long ago and is now deceased.
History
Early history
She was going to marry Beauregard on the Delta Queen, but she left him at the altar when she thought he had stolen her emerald necklace. In fact, the necklace was stolen by the captain of the Delta Queen, a rival for her affection, and hidden in the steering wheel of his ship in order to ruin the wedding.
The New Scooby-Doo Mysteries
Ghosts reunited
Her real ghost appeared after Beauregard was posthumously cleared, able to be reunited with the ghost of her love at last.