How Can Bipolar Disorder Be Diagnosed?

My 47yr old sister, a dental hygienist, has ID d herself (from web info only) as possibly suffering from a bipolar condition which may be treated with lamictal. She takes generic ritalin, about 60 mg daily, and also takes cymbalta for depression and pain control . She is employed, pays cash to a physician who sees her in office for Rx management only, as she has no insurance. She had a talk her employer, one-on-one, in private and the employer (her dentist) , thinks my sister is maybe rapid-cycling and has quite possibly been unaware of her behavior as it appers in the office setting. She plans to see her physician this week to discuss lamictal. Suggestions, Please!