If your instinct is that it is a habit at night, what about talking to her to explain that she can have a cup of water in her room but that once it is empty that is it until morning, and working using ST. techniques if she wakes and cries for more in the night.
This way, you're not restricting her from drinking, if she really needs it. You're not maintaining the prop of calling you for more water, and you're reducing the amount when's taking over the nighttime.
I do agree with others though, try not to worry about the PTing yet, this will happen when she's ready, and stopping/reducing night drinking now may have no effect in the longer term.