Is there any meaning or hidden message when a woman wears her wedding
ring on her pinky finger of her left hand?

Maybe she has gained a lot of weight since she was married, and the
ring no longer fits her ring finger?

Here's some interesting ring lore:

"The following is the language of rings, and applies both to a man and a woman. 

Ring on the first finger of the left hand: I want to be married.  
Ring on the second finger of the left hand: I prefer platonic friendship. 
Ring on the third finger of the left hand: I am engaged or married. 
Ring on the fourth, or little finger of the left hand: I never intend to marry."

http://www.vangelis.com.au/lovesuper.asp

I'm inclined to agree with Pink's first suggestion. Another way to
find out the answer.... ask her.

Nenna-GA
GAR