Hazel Kent, 40, of Bracknell, Berkshire, claims the operation is her only hope to lose weight, the BBC reports.
Ms Kent lost seven-and-a-half stone (49kg) in 2001 after having a gastric band fitted but it had to be removed due to medical complications.
Berkshire East NHS PCT said Ms Kent's body mass index was not high enough.
Its guidelines state anyone undergoing the surgery should have a BMI of at least 50, while Ms Kent's is 37.8.
Ms Kent, whose weight is now 15st 10lbs (100kg), said if her bid for a judicial review was successful at the High Court in Manchester in October it could make legal history.
"It's definitely been worth the fight," she added.