4yr old won't stop wetting at night - Even before she is asleep

My 4 yr old daughter has been toilet trained since she was about 2 1/2 yrs old, but she has never once woken up with a dry nappy. I have tried waking her up through the night, and she probably woke up dry only once. I have tried putting knickers under the pull up, I have tried leaving her in a wet bed, I have tried stickers, special days out, special treats, and she seems excited to try but never any success. Last night I tried the knickers under her nappies again and she just weed in them while she was still up. She knows this is wrong and does not seem to care whatsever!! I am feeling totally disheartened now and not sure what to do. I told her tonight if she can wake up dry tommorrow we can go to the zoo, she seems really really excited but now I am thinking I am just setting her up for heartbreak in the morning. She is really good during the day not a worry at all.