L.G.
Try putting a clock/radio/CD player in her room with the wake-up set to whatever time you think is appropriate for her to awaken to soft music. Then tell her that she has to stay in bed with the lights out until she hears the music.
If she's just switched to a bigger bed, it might be that she wakes because she doesn't feel the "snugglieness" of the crib, so you might try putting some pillows on either side of her in the twin bed--or big snuggly stuffed animals.
Best of luck.