Watermelon is great as it contains alot of liquid. If you put liquid in her bottle during the day will she drink that? Juice in the form of tetra packs are a good (bribe) as they are different. At the start of each meal offer a drink before food as sometimes they are too full after a meal to drink. Also at meal time a special drink like you have, juice, can sometimes do the trick.
The icypole idea is worth a try, just freeze juice, yoghurt etc.