Good job! It is time to take some stands and let her learn to deal with them. She will either drink the milk or not. If not, make something you like out of it, drink it yourself or stop buying milk all together. Take a look at the other things she demands to see if you can change them also.
If she adds it to your list of abusive and neglectful behaviors, congratulate her on her flair for the ridiculous and feel satisfied that you have given her yet another step towards that "Mommie Dearest" expose.
Or give her a book like "A Child Called It" and let her see what REAL abuse is.
Or both.
My kids have been told to feel FREE to report me for abuse/neglect. And to have a bag packed and be ready to leave for good when the social worker gets here. I have refused to let them throw that in my face. They can either call and tell someone at child protection or they can tell their friends. But they can NOT toss it in my face. I take LOTS of privileges away for tossing accusations of neglect around if they are unfounded in the eyes of reasonable adults (meaning NOT their gma).
It is something you may want to consider. Be SURE you will take that step if you say it though.
anyway, Way To Go!!! Kudos for taking this stand.