Right now, she is using the bottle as her transitional object to help her fall asleep, and that's not a habit that you want to encourage. When children fall asleep sucking on a bottle, they often have the bottle in their mouth for a long period of time. This can lead to significant problems with tooth decay because the milk is bathing the teeth constantly. If you feel you must give her a bottle to take to bed, then put only water in it.
My general advice is to eliminate the bottle "cold turkey": Pick a day to do it, remind her a day or two before, then throw the bottles away on that day. Your daughter may then need some help developing another way to comfort herself as she learns how to fall asleep on her own. A favorite blanket or doll may be useful.