It sounds like she might be afraid of something. At the age of 3 is when imaginations start to really take off, but they can still have a difficult time telling what is imaginative and what is real, and she may also not know how to articulate why she is crying to you. At this age is also when kids don't want to stop their day to sleep, they want to keep playing or interacting with Mom and Dad, and sleep seems really awful. When my daughter was 3 is when she started coming up with numerous reasons to stay up, saying she was thirsty, that she was hungry, that she had to go to the potty, that she had to find something, etc. 3 is actually a very trying age, personalities can suddenly seem to change and they can really test your patience, and yes, break your heart by crying for 30 minutes. Try changing her bed-time routine a bit and see if that helpss. I just read that TV can keep kids from falling asleep, even if has been a couple of hours since the TV was turned off. Try playing a quiet game, then offer her a light snack, like a couple of crackers and a bit of milk (a snack eliminates the I'm hungry or thirsty excuse to get out of bed), then have her do the normal potty and burshing teeth, washing face routine, then read a calm story and put her to bed. Even though it's extremely difficult, do not keep responding to her crying, that only reinforces it. Go in once or twice, pat her on the back, give her a kiss and tell her it's night time, but after that you should ignore her crying and she will eventually go to sleep, and although it is very trying, this will pass in it's own time. Good luck.