After 12 months babies don't need either formula or cows' milk. They can get calcium from other sources - 3 serves a day of dairy sources such as yoghurt and cheese or there are plenty of other sources such as brocoli and pine nuts, as well as other milk types - goats, rice etc. So personally, if the milk is upsetting your child, I would recommend not giving it at all. They can drink water, and just make sure their diet includes enough foods for them to get their calcium allowance. There are lots of kids out their with dairy allergies/intolerances that get plenty of calcium without dairy.

Ngala, you can just try her with straight cows' milk, it doesn't need to be mixed or diluted.