There's no reasonable answer can be given to this just yet, at least so far as the movie canon is concerned.
There is however a parallel in the books, following Gandalf's first encounter with the Balrog in the Chamber of Mazarbul:
I am afraid Balin is buried deep, and maybe something else is buried there too. I cannot say. But at least the passage behind us was completely blocked. Ah! I have never felt so spent, but it is passing.
Gandalf refers this this again when the company finally see the Balrog:
'A Balrog,' muttered Gandalf. 'Now I understand.' He faltered and leaned heavily on his staff. 'What an evil fortune! And I am already weary.'
It's evident therefore that (in the books) use of power is tiring, and since (in the movies) Galadriel uses the most power against the strongest foe, it follows that (assuming the script-writers had this in mind) she would be the most drained.