baby not sleeping

My little girl is 1 1/2. Usually she does to bed at 9, wakes up at 9. Well last night was a long night, she was sick and for some reason she was WIDE AWAKE until 1am! Yep. 1am. She finally went to bed and now it's 6am, she's up and screaming. It's not pain crying. It's her normal "I'm awake let's go" cry. But I can't let her get up with only 5 hours of sleep when she always gets 12.