It's possible that "Sophy Gray" was a composite figure or a fictional creation used by Pre-Raphaelite artists. There is no known biographical information about her, and no historical records or evidence suggest she existed as a real person.
The confusion might stem from the fact that some Pre-Raphaelite paintings depict women with the name "Sophy Gray" inscribed on them, like "The Beloved" by Dante Gabriel Rossetti. However, these could be fictional names used for artistic purposes.
Therefore, it's safe to say that the birthdate of Sophy Gray is unknown, and her existence is uncertain.