My LO is 20 months old and still takes a bottle of milk before bed. With baby #2 due in less than 2 months, I'd ideally like to get her drinking her nighttime milk out of a cup before her sister arrives so that there's no association between her bottle being "taken away" and the new baby getting one (I intend to breast feed but will pump and give a bottle per day from a few weeks old so that hubby can participate in feeding).

The reason I'm scared is that when I tried to transition her from a bottle to a sippy/straw cup for daytime feeds, she dropped all daytime milk and now only has water or diluted juice from her straw cup. I'd hate to have the same thing happen at night - while she eats a lot of yogurt/cheese during the day, I feel like she really needs the extra calories from the milk at night to get her through.

Any advice on how to make this transition as trauma-free as possible and still keep her drinking milk from parents who have been there, done that?