It depends on the size of the hernia, the position and exactly which tissue layers are involved. I would always opt for surgical correction to avoid problems - without a solid seal around the organs they can become twisted/compressed if they become trapped within an open hernia ring.
Some very large hernias can be difficult to repair and need implants to act as an artificial muscle layer but very few cannot be remedied by surgery. Sometimes surgery isn't 100% successful the first time round. Talk to your vet as to whether there were any factors that led to an unsuccessful operation and whether these could then be avoided, and see what the reasons for reluctance for further surgery are.
on a separate note, she should not be bred from as many hernias have been demonstrated to be inherited. I often spay/neuter the animal at the time of surgery to avoid multiple ops and make sure there is no chance for breeding later on once surgery has removed the outward signs of a problem.