Leah,
I had the exact same problem with my then 3 year old son ( which is now 12 years old). I always gave him applejuice wich is worst ofcourse. Well I had finaly had enough of it after I went to germany to my family and they made fun of it so much.
So one night I just stoped, don't give her any water at all nothing to drink, she does not need it, she has to learn to manage to just sleep. The first night was really really bad with lots of tandrums and crying on both sides, then the second he only woke up once and when he figured out I would not give him anything he went back to sleep and that was really all there was to it. Just really stick to it and don't give her anything to drink and it will work for you within two days tops.
Petra.