I have been using Flickr now for years, constructive criticism is always welcomed and normally done via flickr email, not via comments.
If you put criticism on comments its like giving someone a public telling off, surely its better to take them to one side and say what the good points are about a photo, say what you think is wrong with the photo and how to correct it and leave it up to the tog too see if they take your advice or not.
Would any of you like your boss to shout at you in public or would you rather be taken aside?????
I see from the flickr users profile that she has been doing photography since March 2009, IMHO she is doing brilliant work for a photography newbie. I also see that the image under criticism has made FLICKR FRONT PAGE, #17 when I looked just now. Although it is under exposed, she obviously likes it and does many other people who viewed commented and added it as a favorite to get it to flickr front page..
http://www.flickr.com/photos/raffertyevans/3783531023/