I understand the struggle that you are going through. My daughter who is now 10 years old was the exact same way. However, it is extremely important for you to break that habit that she has. She is at the point now that she may be ready to potty train and not giving her fluids at night may not be too bad an idea anyway.
My fear is that what happened to my daughter will happen to yours. She had gotten to the point where she had to make many painful trips to the dentist and get many of her teeth pulled out. It was so bad that they were measuring her mouth for baby dentures because so many teeth were missing they wanted to make sure they grew back in straight.
My daughter was only three at the time all this was happening.