She should be 1 before she has cow milk. Keep in mind that cow milk is not a formula replacement. Formula is meant to be replaced with full balanced meals. Cow milk can be part of a healthy diet, but a full bottle a day is a lot, assuming she eats other dairy products throughout the day. There is no reason to ever transition from formula to milk, but if you want to phase out formula, you can alternate giving her a bottle of cow milk, almond milk, soy milk, etc. For some babies, even a bottle of warm water works.
Definitely wait the month or two until you start to ween. And yes mixing is the best way to go. Say if your baby is doing 8oz feedings you’d want to do 2oz milk for a bit over a week, then add 2 more ounces and do that for a bit over a week then so on and so forth
When she turns one, start by offering a small amount of milk in a sippy cup. Since most formulas are milk-based, the taste should seem familiar. If you have other kids, pour milk for everyone at the same time and let her see you pour hers too—babies love feeling included! If she’s hesitant, try mixing a little milk with her formula and gradually increase the milk ratio over a week or two. Warming the milk slightly can also help if she prefers it closer to body temperature. With my kids, I waited until they turned one before switching. My first was breastfed and had milk while still nursing at night. My middle child was formula-fed, and by the time she turned one, she was ready for milk since she was eating solids and drinking water. Take it slow and follow her cues!
Start giving small cubes of cheddar cheese or any cheese, then if no allergies arise give half and half for a few days and then only milk
She should be 1 years old for milk as I know.