As she is 12 mos, you can do it right now. How is she with a sippy or cup? Will she take some milk in it? Does she have other sources of dairy? Between 1-5 yo, it is recommended in Canada that children should have 2 servings of diary (500mL or 2 cups of whole milk; cheese; yogurt; or calcium fortified juices/soy; etc"
If this is her first taste of whole milk then it may take some time (days or weeks depending) for her to get use to it. There are several ways of transitioning to whole milk:
- cold turkey
- add a little bit of whole milk into her bottle/sippy until it is 100% whole milk.
- introduce whole milk as part of the meal in a sippy/cup and slowly decrease the amount of formula in the bottle.
How is her diet? Is she eating a variety of meats, veggies, grains, dairy & fruits? If her meals are balanced and she is getting 2 servings of dairy (cheese/yogurt) then don't worry too much about a strong dislike to whole milk in the beginning. Keep offering whole milk and decrease the formula.
HTH
BTW I'm moving this over to Eating for Toddlers. For toddlers, usually there are 3 meals plus 2 or 3 snacks - do what works for your family. So what you have is fine except maybe offer food before milk.