I just picked the nursing session my kids seemed least attached to- usually one that was not associated with a nap or bedtime. I would offer a sippy of milk for that feed and then about 3-4 days later, do it with another one. Keep the most important nursing (like if you nurse her to sleep or whatever) for the end. Don't expect that they will fully replace the nurse with the milk right away. But in time, the milk intake will increase and you will see the interest in nursing wane. It will take a few weeks- it took us about a month or so to completely give it up, because I wanted to do it gently.
M, mommy to A 2005, E 2007, and L 2010