Izzy went through it recently - and is again back to normal
What I do is hold the door - if she can't get out she gives up...otherwise she would have been up hours! At first she went mad, banging and throwing everything in her room...and each day it got less and less...to the point now she either doesn't get out or just tries the door and then gets in bed!
I actually have to have my dressing gown tie around the door handle lol, and pull it tight and then stand on the stairs with it - so when I can hear she is in bed and going off I can let go and creep down the stairs...our house is the creakiest ever and trying to get down the step by her room, through the stairgate with our her hearing was impossible! Once she is asleep I can go up there and even in her room and she doesn't wake, but for the first few minutes she will wake if she hears me!
Dan suggested we put a lock on the door which I thought was not nice at all, this way the door is closed and she can't get out, but the minute I go down the door opens again, so if she wakes she can get out - I'd hate her to thinkshe woke up and couldn't get out