I still have the guide sheet my pediatrician gave me. It clearly states 4 servings at 1/2 cup each. THIS IS WHOLE MILK ONLY. I was expressly told not to give anything but whole milk until he was 2 years old.
The guide sheet also states that you can give your child unlimited amounts of breast milk or formula.
That is pretty specific information and I would definitely not short her from formula if you are drying up. Don't be too anxious with the cow's milk.
According to the chart, you may be a month early on cow's milk, but that is not going to make a noticeable difference. Each child's development is different. Some children teeth a lot later, etc. These guides that are out there are 'blanket' guides in helping us first-time moms. So, like I said, a month difference, NBD.
Start introducing more water as well. It is good to start getting into the habit now of having a sippy cup of water sitting around for her to grab and sip at will.
Good luck! :o)