Vitamin/Mineral Deficiency and Fatigue

My wife has brought it to my attention that she feels she has a vitamin and/or mineral deficiency that is causing her extreme fatigue. Despite getting enough or more than enough sleep, she wakes up drained.

Aside from getting her on a good multivitamin and mineral, what specifically should we look into getting her to supplement with to see if we can get her out of her lethargia?