yes, just let her hold it and get used to it for fun, dont worry if she doesnt know what to do yet, all of a sudden, you turn around and she will be drinking from it, but it may be months. esp not sitting on her own, it would be more to just let her touch it.
if you bottle feed, i would go for the nuby cup as the soft spout is very similar to a nipple. then when she gets a little older, just try the straw ones at 18 months. they are a favorite of my daughter. and if you bottle feed, yes just give her water. i also love the foogo cups from thermos if you were giving milk and needed to keep it cool for travel.
if you breastfeed, are you wanting to transition her to something other than the breast. if you want to have another way of feeding, then put breastmilk in it. it would be the same as getting the baby used to going back and forth between breast and bottle.
otherwise, if you just are wanting to get her used to it, but are nursing only, then give her water. again, go for the nuby. the handle cups are great for little babies, but they grow out of them quickly, they are a pain to travel and store, and im not a fan of the spout selections.
there is absolutly no need to give her juice. it is the number one reason children have so many cavities. then they start to ask for juice instead of milk or water. my daughter is 3 1/2, no cavities, no problems. to this day, she has probaly only drank juice 10 times. i give her water or milk mixed with water. give the actual fruit instead. good luck!!!