Sabrina is a Psychic-type Gym Leader in Pokemon FireRed and LeafGreen, the remakes of the original Pokemon Red and Blue games. She is not part of the original Kanto games, and therefore does not appear in HeartGold.
In HeartGold, you will encounter the original Kanto Gym Leaders in their original locations. This means you will face:
* Brock (Rock-type) at Pewter City
* Misty (Water-type) at Cerulean City
* Lt. Surge (Electric-type) at Vermilion City
* Erika (Grass-type) at Celadon City
* Koga (Poison-type) at Fuchsia City
* Sabrina is not part of the Kanto Gym Leader line-up in HeartGold.
* Blaine (Fire-type) at Cinnabar Island
* Giovanni (Ground-type) at Viridian City
If you'd like to experience battling Sabrina, you'd need to play Pokemon FireRed or LeafGreen.