Toddler up until 1am????

My step-daughter is 17 months old and last night, (we have her friday-monday) we put her to bed around 8 like we normally do and ordinarily she'll cry/scream or doze off pretty much right away but when i went back in about fifteen minutes later to get something, she was sitting up in bed with her blanket over her head at the far end of the crib just staring at the door.

My husband and i decided that we'd let her stay up a little bit, we don't normally but neither of us had ever seen her do that plus we knew there was a possibility that she had just had a four hour nap before she was dropped off at our house (at 6). So we kept her up until nine and she still wasn't sleepy at all- even after running around and playing with me and her daddy, so we decided to keep her up until she started acting at least some-what tired but at ten she still hadn't so we went ahead and put her to bed, we were ready for her full-fledged screaming tantrum (which usually gears up while we're taking her to bed); but it never happened we assumed she just fell right to sleep, but when i went in at midnight to make sure the monitor was on and to check on her she was still wide awake- just laying there quietly and sat up when i came in. Me and my husband made sure the curtains were closed good, turned off the nightlight (its fiberoptic and changes colors), turned off the hall light, and kept our conversations low. Around one when we went to check on her she was finally asleep.

This morning she woke up around 10:30 and has went back to sleep.

I don't like having her sleep schedule so messed up but i'm not entirely sure what could have caused the problem, whether its normal or something to worry about. Or even what to do to get her sleep schedule back in order