Is there medicine or anything else my wife can take, to want sex more.?

Probably. The first thing to do is see her doctor to discuss this issue. If there is a specific reason for the decreased libido (menopause, oral contraceptive use, pain with sex, mood disorders, medication side effect, etc) it can be addressed directly. This is a fairly common complaint and many women are reluctant to bring it up with their doctors, but in most cases improvement is possible and likely.
No specific therapy. This site may help you. Treating female sexual dysfunction needs a multidisciplinary approch. First find the cause and then treat it first. This site may help: http://www.Mayoclinic.Com/health/female-sexual-dysfunction/ds00701/dsection=treatments-and-drugs.