I would strongly recommend to your dentist that she read the medical journal articles that have been published putting forth guidelines on dental
anesthesia and POTS if she has not done so already.
For example:
Brooks, John K., DDS and Francis, Laurie A. P., RDH. Postural Orthostatic Tachycardia Syndrome: Dental Treatment Considerations. J Am Dent Assoc 2006, Vol 137, No 4, 488-493.
http://jada.ada.