Get her a different type of sippy cup, that will be used JUST for milk. Maybe a sippy with a built in straw?
A technique that "Suppernanny" uses to break pacifiers (that I'm sure would work for bottles) is; to explain to your child that there are babies in the world who NEED bottles, and don't have any. Then have her help you collect all her bottles and put them in a bag, then leave them at her bedroom door (or where ever) overnight. Tell your daughter that the "bottle fairy" will come pick it up at night, and bring them to babies who really, really need them - but the fairy will leave a little surprise for your daughter in return, to thank her for her generosity.
The 'surprise' could be the new sippy 'just for milk' plus a little toy, or something else you think she would be excited about.
The important thing is that the "fairy" (you) get RID of the bottles completely while your daughter is asleep, to make sure that she believes the whole story, and also to make sure you don't end up going back to them in a moment of weakness. If they are out of the house, then she will soon learn she doesn't even have the option of using them anymore. "Out of sight out of mind" kind of.
She might ask a few time for the bottles, but just remind her that she did a really great thing and gave them up to the babies... Make her feel good about it. Soon enough, she'll forget about them completely! Good luck.