L.P.
I had the same problem with my son when he was about 1... it seemed to me that when he would stir in the early a.m. and see it was daylight, he would immediately decide to get up. I got a brown lightweight throw blanket and put it over the window, so it literally looks as though it is night in the room all the time. This worked like a miracle. He would stir or wake a little and believe it was still night, so he would allow himself to go back to sleep. Of course you can buy room darkening shades (which in my experience don't work that well) or heavily lined drapes (they work ok), but a dark colored throw is a cheap, temporary solution that you can clip to the curtain rod with clothes pins, or thumb tack to the wall if you aren't too squeamish about the little holes. It's easy, cheap, and completely removable if you are getting company or something and don't want a throw hanging on your window!
Amy J will tell you to fill your kid up with healthy food all day long to ensure she is not waking due to hunger... that may work too, but maybe the two things in conjunction will work wonders! Hi Amy... :)