A.C.
hi~
on the back of the formula can it should tell you (e.g. on the back of the can of Bright Beginings it states for a 2 ounce bottle use 2 counces of water and 1 scoop of powder). thus you would go buy the amount of water before adding the formula.
As far as how much she should drink here is some info from http://askdrsears.com/html/0/T000100.asp#T031009
HOW MUCH FORMULA DO I FEED MY BABY, AND HOW OFTEN?
As a general guide:
Between birth and six months of age your baby will need an average of 2 to 2.5 ounces of formula per pound per day. So, if your baby weighs ten pounds, she will need 20 to 25 ounces per day.
• Newborns may take only an ounce or two at each feeding
• One to two months: 3 to 4 ounces per feeding
• Two to six months: 4 to 6 ounces per feeding
• Six months to a year: as much as 8 ounces at a feeding
Small, more frequent feedings will work better than larger ones spaced farther apart. Your baby's tummy is about the size of his fist. Take a full bottle and place it next to your baby's fist and you'll see why tiny tummies often spit the milk back up when they're given too much at one time.
IS BABY GETTING TOO LITTLE OR TOO MUCH FORMULA?
Signs that your baby may be getting too little formula are:
• slower-than-normal weight gain
• diminished urine output
• a loose, wrinkly appearance to baby's skin
• persistent crying
hope that helps :)