The bottle and formula can cause bottle rot. I was told to put cold water on a wash cloth and let them chew. It helps to clean the teeth and soothe the gums
Give her the toothbrush and let her chew on it herself, I sing a little song when I do my daughters she is 15 months and use floride free toothpaste that she loves
It's not gonna rot her teeth unless sugary drinks are just sitting on her teeth. But maybe Try rewarding her , or brush your teeth when you brush hers