The Pradoshamahatmya section in the Shivapurana mentions this Gandharva princess, when Suta talks about Pradoshamahatmya to rishis at Naimisharanya.

Satyaratha, a Pandya king was once observing the pradosha vrata. Due to flaws in the ritual, he died and reincarnated as the king of Vidarbha, but died in a battle with the king of Salva. His pregnant wife escaped into the jungle, and there, gave birth on the banks of a river. Later, as she went into the river, she was caught by a crocodile. A brahmin woman called Usha, and her son, Shuchivrata came by that way then.

Seeing the child lying alone on the riverbank, they took him and named him Dharmagupta. Later, as per the advice of a brahmin named Shandilya, who lived in the village of Ekachakra, both Shuchivrata and Dharmagupta undertook the Pradosha vrata Lord Shiva was pleased with their devotion, and gifted them a lot of money. Later, Dharmagupta fell in love with Amshumati, the daughter of Dramila, a gandharva, and soon they were married.

Because of the Pradosha vrata’s benefit, Dharmagupta and Amshumati were succesful in defeating the Salva king and regaining the throne.