My otherwise healthy 60 year old mother is not eating

My mother has always been underweight.  At 5'9" I doubt she's ever weighed in much over 130lbs, but being very tall and thin runs in the family, I’m 5’8” and run around 125.  In recent years she's become even thinner, to the point that our family is very concerned. Currently, I would guess that she is down to around 110 or below and looks gaunt and extremely unhealthy.  While she is now 60 and retired she continues to be very active but is just not eating.  As a lifetime smoker, her breakfast consists of coffee and a cigarette, lunch is usually skipped, and dinner is 1/2 to 1/3 what an adult portion should be.  She has struggled and been medicated for mild depression for years and I am very concerned that this psychological issue has worsened and she is somehow punishing herself by not eating.  All I can imagine is some sort of non-vanity anorexia.  I have spoken with her on this topic and my father routinely attempts to make her eat the first two meals of the day, to little avail.  We have decided that it is time for a more severe intervention to change her eating and smoking habits, but I'm not sure what the best way to do so is, as I live many states away.  
Advice is appreciated,
JM