A typical complex partial seizure should not result in a fever. However if a seizure has a significant amount of muscle activity or jerking then a fever can occur. Another thought could be that the seizure was secondary to a febrile illness which was just presenting itself. However, you should have seen signs of this after the seizure.
Regarding the change in her seizure, you did not state how recent the VNS was placed. If it was placed recently, the new seizure type could be secondary to either the medication or VNS partially preventing her typical seizure. If this was an isolated seizure then there may not be a need to repeat the EEG. However, if the quality of her seizures has continued to be different then re-investigating would be reasonable.
Lastly, if she is still having seizures despite medication and VNS you may want to explore other surgical options. For this I would recommend that you have a consultation at a large epilepsy surgery center, such as the Cleveland Clinic, for an opinion. Good luck.