I am assuming she is bottlefed given that you've been advised to give her water? Otherwaise they'd normally get you to drink more, and feed more often.
I don't htink I'd add anything to it, maybe pedialyte? but I'd check first.

Milo was really slow on the uptake (or intake? ha ha) with water, he hated for quite a while.

He still will not drink it from a bottle, only a cup.