Oh! my daughter was exactly the same as yours. She stopped formula milk when she was 1 yr old. She hasn't take it since then. And I gave it up already. Yet still, I use some formula milk for the cereal. but she only takes it only once or twice a month. I feed her fresh milk then. At the beginning, she doesn't take much, but now, she can take one in the morning. i feed her 'smart milk' becoz it is with DHA.
And nurses said that it was fine for her. Just kept feeding her a balanced diet would be fine. And my daughter is fine up till now. But my daughter will have breast milk before sleep every night.
Yet, i think you should try to mix the formula into her food. You can make pancake with formula milk. Mix formula milk with cereal, cornflakes..... or even to add in some Horlick. My daughter didn't accept any of the above@@ She just hated the formula milk. She rejected any of those. So.. I just give her fresh milk now.