We tried to give DD expressed milk in all sorts of different ways when she was about 3mo - nothing worked, if anything went in it just got spat out! But she took it in a cup from DH at around 6-7mo, it has a spout but actually DH found she took it better with the top off to start with, just drinking from the rim of the cup, was a bit messy but once she recognised what was in the cup she was happy to use the spout with less spillage. We did this for her second feed of the day while I was out, maybe easier than at bedtime? I'd suggest that if she's been getting really upset, you could leave it a week or more and try during the day, unless you're in a hurry? You could even try a cup at 5mo. What do you,think?