In 2375, the USS Voyager encountered a bio-plasmic organism, which read the crew's thoughts and created exactly what they wanted to see: A way to return to the Alpha Quadrant. Among the things it created to make them believe they were headed towards the Alpha Quadrant (when in reality, they were heading down its digestive tract) were letters from friends and family.
Among the letters was one written to Seven, from an "Aunt Claudia". She later turned out to be a fictional creation of the organism. (VOY: "Bliss")
It was later revealed Seven does have an aunt on Earth, the sister of her father, namely Irene Hansen as given in "Author, Author".