N.G.
As the other mothers have pointed out allergies are an issue but something to think about even more is the possible long term effects of getting her used to drinking something so sweet. Would she be drinking this from a sippy cup? If so it could cause damage to her tooth enamel and worse disrupt her willingness to drink plain water.
My daughter suffered from chronic constipation as a young toddler and the doctors told us to do anything to get her liquid intake up. The only thing that worked was mixing a bit of apple juice with water. She is now six and still does not really drink water on its own. I think it would be much better to work on getting her to eat veggies by finding dips she likes - like peanut butter on celery or hummus with carrot sticks etc. - there is usually something you can find that will work if you keep trying (boring I know) and you don't give sugary sweet stuff as an alternative.
Also I think sneaking a few veggies in other things here and there is quite all right - and this is why: If it means you stop worrying about it and can secretly smile, the change of atmosphere at mealtimes is so extraordinary that your daughter might relax enough to start trying the things you never imagined! I put pureed cauliflower in mashed potatoes (even my husband doesn't notice) and pretty much every vegetable going in Bolognese and then I serve more veggies on the side and they just have to have two bites of everything. I also so do homemade popsicle sticks that are just fruit mixtures in the blender that I often add carrots or cabbage to (it makes them smoother and they taste nothing!) I am happy because I know they are getting something and they are happy because they think it is not too much!
I wish you the best of luck!