S.F.
I don't think there's any need for formula if she's eating all solid foods. She's getting her nutrition from a balanced meal. I would start transitioning from all drinks at bed time. Only give her water at night. This will help prevent tooth decay and desiring the midnight snack.
Maybe after a month or 2, take away the sippy at night altogether. My 2 and 3 year old started sleeping with the sippy, and they didn't even drink from it. They just liked knowing it was there... like a safety blanket. My 2 year old still tries to sleep with a sippy. I put about 2 oz of water in it, and then he just sleeps with it. After he's sleeping, I take the cup back to the kitchen. It's good to work away from drinks at night so potty training is easier and you don't have midnight leaks.
I give my 2 and 3 year olds about 6 oz of whole milk with a meal. I give them juice at snack times, and water any other time.