I just posted this for a 17 month old, but similar things apply I guess:
QUOTE
All patterns of eating, sleeping, behaviour, contentedness, etc will change and evolve as children get older, learn and experience more, and gradually become more independent.
So you can't expect things to remain the same for very long. Try less naps during the day, make sure bed-time is relaxed and happy, and maybe keep her up a bit later. Give her a doll or teddy for company in bed, or a special blanket, or whatever.
UNQUOTE
Make sure she isn't hungry, but also don't over-feed before bedtime. Make the evening hours before bed relaxed, no TV or busy activity; read her a little story, of just talk about the day's events, and what she can do tomorrow. Have the room a suitable temperature, and ventilated. Try keeping her up later, though that may not be possible depending on your other commitments/priorities.