Babies and toddlers shouldn't drink juice anyway, so no need to worry about that. If she's happy drinking milk and she's not overweight or drinking an excessive amount of it, then I wouldn't be too concerned about her only drinking milk. It's good for her and she's obviously getting plenty of hydration that way. I found that giving a sippy cup or an open cup (like a doidy cup or just any open top cup) in the bath to play with helped my daughter learn to drink water from a cup. Until we switched to using a real cup (not a sippy cup with a lid, she didn't drink much though), but she drinks from a normal cup just fine. It's just practice. I'd give her a cup at every meal, in between meals to play with, in the bath, etc. She'll eventually work it out.
