Riker: I could have saved that girl.
Picard: You were right not to try.
And what were the consequences that would have happened if Riker had brought that girl to life? I don't know. Maybe a slight gratification and sense of happiness that he helped a little girl live? There wasn't any "The girl or your crew!" situation going on where there were things at stake. Just some grumpy old man telling him that power corrupts and doing things easily is a sin!
My thought - it happened, she died, she was dead, and it would have been "wrong" to undo what otherwise could not be undone.
To me, it seems to kind of point to belief in or support of "fate" or "destiny," that she was supposed to die there, then, and it would have been wrong to undo that.
And if Riker can use the power of Q to bring back the dead, then - what can't he do?
And Q is hardly a model to be put up for the responsible use of absolute power. The Q, as we come to know, are more like bored children roaming the galaxy, pulling the wings off flies for their own momentary amusement.