"Lestat’s mother, a noblewoman of breeding and education, brought into the Blood by her own son in 1780 in Paris. A wanderer who dresses in male attire. A familiar figure in the background throughout the Vampire Chronicles." 
She had yellow-blond hair like her son's and cobalt blue eyes with "too small, too kittenish" features, as Lestat described them, that "made her look like a girl."
Gabrielle came from a prosperous Italian family. She was educated and had traveled to and lived in many cities in Europe. Then she was married at a young age to Lestat's father, the Marquis d'Auvergne. Gabrielle gave birth to seven children, but only 3 survived. Out of these sons, the youngest (Lestat), was to become her favourite. She and Lestat shared a special bond: they both were trapped in a place they hated and struggling endlessly to escape.
Gabrielle was cold and uncaring to everyone. She was the only person who was educated in her family and read her books every day, yet lacked the patience to teach her sons to read or write anything. Over the years she sold two of her heirloom jewels from an Italian grandmother to aid Lestat, the only person she loved and cared for. She lived life through him; he was the male part of her. She suffered a rapidly declining health due to bad winters and multiple childbirths. It eventually developed into tuberculosis.
She funded Lestat's trip to Paris with his friend Nicolas de Lenfent by giving him one of her rings to sell and advising him to hitch a ride on the postal carriage. Lestat became an actor there and was far happier than he ever was back home. He was grateful and loved his mother for all that she had done for him over the years so he sent letters to her telling her about his life in Paris. She encouraged his acting career, which gave him much strength and further confidence. She carefully hid her rapidly declining health to keep him strong.
Lestat was made into a vampire by Magnus, and inherited near-inexhaustible wealth when Magnus killed himself in a bonfire. He repaid those who helped him with gold and indulged in his new-found wealth. To hide the truth from Gabrielle, Lestat told her tales of going to the Bahamas, marrying a rich woman and coming into vast wealth. Intrigued, she went to Paris to see her son before she died. Lestat went to see his mother the second night she was in Paris and tried to hide the truth from her, but she found out upon closer inspection of Lestat's changed appearance that he had become a vampire. When Gabrielle literally began to die right before his eyes, a desperate Lestat made her a vampire.
Lestat was now the maker, parent, and teacher, while Gabrielle became the fledgling, the child and the student. Lestat took her to his tower where they lived happily for months. Things changed, however, when Lestat destroyed the Satanic cult headed by Armand, founded a theatre and made Nicolas de Lenfent into a vampire. After this, Lestat and Gabrielle went traveling around the world. Gabrielle became increasingly distant and cold to her son. They finally parted in Egypt just after the French Revolution. Gabrielle went into the deep jungles of Africa and Lestat went underground to sleep for two years.
Gabrielle was off exploring the world on her own for the next 200 years. She did not reappear until 1985 (during The Queen of the Damned.) She was there to help her son fight against Akasha and help save the world. During this time, she developed a slight bond with Marius, but nothing became of it and she drifted away from everyone again. Gabrielle resurfaced for the last time after Memnoch the Devil, in The Vampire Armand while Lestat was in his catatonic sleep.
Although androgyny is a common theme in Rice's books, Gabrielle showed many behaviors that implied that she had genuine gender-identity issues. She often referred to Lestat as her phallus, and lived her life through him. After Lestat made her into a vampire, he procured for her an extravagant dress to replace the blood- and excrement-stained one she died in. Only moments later, she killed a man, discarded the dress and took his clothing for herself, tucking her hair beneath a cap. Some time after, she cut her hair to a length more befitting a man and was the next night horrified and shaken when she found it restored to its original length. As the story moved on, Lestat described her candor and comportment as that of a man, though her girlish facial traits kept her from carrying off the ruse successfully. He goes on to note that she only ever rarely donned dresses again, and that when such events did occur, they were only done to please him.
Gabrielle has only appeared in the Broadway Musical Lestat played by Carolee Carmello who was nominated for a Tony Award for the part. In the musical, Gabrielle differs to the book version as she gives consent to becoming a Vampire.