If he was just meaning to go along with the solids- i wouldn't bother using the bottle, but just give her the sippy to play and experiment with. Take out the valve from the sippy if there is one so that she can pour it. Babies are pretty good at regulating their fluid needs, so she may not drink more water if she's getting enough from the formula.
You could also offer it in the bottle you have- is she on thickened formula? does it move slower through the teat?