[Miss Marple]

Several of the Greek Orthodox priests, a couple of cardinals, and several of the dignitaries wore sunglasses.

Sunglasses are often required if you have sensitive eyes, if you are recovering from eye surgery, or if you wish to wear them to hide tears. I find them a neutral item.

[EmilyGeiger]

I figured she wore them to hide tears. Her face was drawn as if she had been crying.

[hoosiermama]

Sunglass are also a must for some when they wear contacts and it is windy/sunny. IIRC Laura wears contacts.