How can I committ my wife to a hospital to start taking her medication? She is Manic Depressant and have been off her meds for a long time.

From what I understand, at least in my state,
She has to consent OR pose a risk to herself or others. Then most often they just keep them for 24 to 48 hr observation and then release them.
You are going to have to find a way to persuade her to take her meds and be consistent about it or leave her go.
What are her swings like? How bad does she get? Are her moods causing a problem with your marriage?