The problem is that night wetting is totally different to the daytime. In the day, they are awake and can develop an awareness of when they need to go and be "trained" by removing the nappy and them getting wet. However at night, the signals from the bladder to the brain do not always develop until as much as 6 or 7 years. So my feeling is that forcing a child to "train" by allowing them to wet the bed every night could just be detrimental and make them feel bad.
Charlotte was definately one who could actually sleep through wetting the bed, she didn't even realise. I remember one night trying without a nappy when she was around 3 (so had been dry in the day for a year), she went to bed at 7pm after a wee, I went to lift her at 10pm and she had already wet the bed and was fast asleep. She then slept until she woke up complaining about being cold at 6am - this was because she had weed sometime in the night and not woken so was now wet and cold. She went back to sleep and woke at 7.30am having wet the bed again.
As you say you think she is saving it up till morning then It might be worth a try doing as Jules said and putting a potty in the room but I think sometimes you have to accept that for some children it can take longer than others.