5 year old tantrums

My 5 year old granddaughter has begun having temper tantrums when she does not get her way.  She is normally a very sweet and gentle child untl she is told to do something she does not want to do, l;ike fo to bed.  She will lay in bed and scream for over an hour and then fall asleep.  
When she wakes up she apologizes for her behavior and promises she will not behave like that again....but she does.

Any suggestions on how to disciplene the child and break this habit?
Cyndy