It seems so long ago
Nancy was alone
Looking at the Late Late show
Through a semi-precious stone
In the House of Honesty
Her father was on trial
In the House of Mystery
It’s likely that this is a romanticized description of a television set; like a quartz crystal. 
 Nancy was suffering from bipolar depression, a mood disorder that, among other things, distorts the way that people see reality. 
 During a manic period, this “looking through a semi-precious stone” would result in a colorful and exciting view of the world. During a depressive period, everything that the person sees would feed into their sense of despair. 
 Semi-precious stones are generally cloudy, implying a hazy view of the world. 

Seems So Long Ago Nancy