The answer to whether Sabrina has a twin depends on which Sabrina you're referring to. There are several famous characters named Sabrina, and each may or may not have a twin.
Sabrina the Teenage Witch
In the popular sitcom Sabrina the Teenage Witch, starring Melissa Joan Hart, Sabrina Spellman does not have a twin. She has two aunts, Hilda and Zelda, who are sisters, but no siblings of her own.
Sabrina, the Animated Series
In the animated series Sabrina, the Animated Series, Sabrina Spellman also does not have a twin. However, she has two best friends, Valerie Brown and Jenny who are often seen together.
Sabrina, the Chilling Adventures of Sabrina
In the Netflix series The Chilling Adventures of Sabrina, Sabrina Spellman has a twin sister, Sabrina Morningstar. This version of Sabrina is a half-witch, half-mortal and her twin is a full-fledged witch.
Other Notable Sabrinas
There are several other Sabrinas in popular culture, but they generally do not have twins. For example, Sabrina Carpenter, a singer and actress, does not have a twin.
To determine if a specific Sabrina has a twin, you will need to provide more information about the specific character or person you are referring to.