My wife has up to 50 mood swings a day, they are extreme mood changes is she suffering from mental illness?

Don't listen to the person above me. Bi-polar doesn't happen daily. The mood swings for bi-polar are over weeks, maybe even months. It could be borderline personality disorder. Suggest that she see a psychiatrist, because it must be terrible to deal with on a daily basis, both for you and for her too.