I think you're mis-viewing the scene. 

 - Elsa uses her powers to make a snow flurry appear in mid-air
 - She then uses the "sweep crossed hands" gesture (otherwise known as the "[no good gesture][1]") to cancels the power holding the flakes up, which makes the ice crystals **fall out of the air**.

There's no particular evidence to suggest that she's *thawed them* when they drop and when we see behind her (a few seconds later) the snow seems unblemished.

It's also worth noting that in the bridge scene, the snowflakes that she brushes off of the banisters simply disappear in a puff of magic. **It's not clear that any of the snow that we see in the film is actually water-based.**


  [1]: http://adayinthewife.com/wp-content/uploads/2013/11/arms-crossed.jpg