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The Kitty's eyes with the pupils so enlarged means that there is something emotionaly that has aroused your cats attention, something very appealing, or something is that threatening.
I will assume since she is not spayed that this may be the onset of her heat cycle that has aroused her senses. Cats eyes can go into a full blown pupil in a matter of seconds. I would not worry about this if there is no discharge, or nictating membrane showing.
I do want to add that if the pupils stay dilated for any period of time I would have your baby into the Vet for a check on Feline Hypertension. This would be the other reason for extended periods of enlarged pupils. Joan