I would comment to my friend as we walked by (loud enough so that she would hear) "It must be so sad to be her, she seems so unhappy".

Next time "She seems so unhappy, I feel so sorry for her!"

People like that cut others down to feel better about themselves. They have the lowest self esteem in the world and they have to point out others flaws or what they THINK are flaws, to make themselves look bigger and better... But it actually makes the look so small and pathetic.... sometimes it makes them look downright STUPID!