Sorry to hear about your little girl
Reptiles are funny that way. I don't know the reason, but they seem to "come back to life". Once at work, a "dead" water dragon was garbaged, and half hour later the little guy was sitting perched on the side very much alive
The locked jaws are normal... the little girl isn't dead yet, and their mouth is one of the last things they let go. Until the moment they are dead, a lizard will typically be resisting you opening their mouth.