does she drink in a sippy cup? what i did was make a big deal every time my daughter drank from sippy cup and emphasize that she's such a big girl na for doing so. we even call it her special cup. we tried also making her drink fresh milk before bed time so that she won't look for the boob.
but ultimately, we were able to wean when my husband and i went on a trip without the kids so she she didnt have a choice.