No, the nutrionist is right. The only thing a baby should get in his/her bottle is breast milk/formula. If you're going to give juice make sure to water it down. I never really gave my kids juice, mostly water in their sippy cups with the occasional small amount of juice to give a little bit of variety to the water.
But back to your dilemma, yes, as soon as you start to introduce solids (6 months) and you introduce something other than milk/formula you introduce it in a sippy cup. There are TONS on the market in various sizes/shapes and nipples to choose from. My kids never took to sippy cups in the beginning, we went straight to drinking from a straw which worked great. Now they drink from sippy cups b/c I can't stand to wash all the parts to the straw cups anymore, but that's just me. But at meals they are drinking from big boy/girl cups (ages 3, and 2)
I have seen other moms out there who have done the same thing as you, and even my sister in law who gives her 18 month old cow's milk out of a bottle. Your child is not going to be destroyed or ruined by this, she's only 7 months old. But better to transition her now than later. Go on ahead and give her water or water down juice in a sippy cup, you may have to trial and error to find the right one that works. Nuby has a soft nipple sippy cup, great for babies who are use to the bottle vs the breast. Try that and dont' give in. She doesn't need the juice anyway...as long as she gets nutrients from her foods and her breast milk/formula (whichever you are using) then continue to encourage water/juice in a sippy cup.
Once she has reached a year and after talking to your pediatrician you can switch her to cows milk. I breast fed both of my babies and both of them transitioned straight to cold cows milk at a year. I still continued to breast feed my son until 14 months so he didn't quite get as much cows milk as breast milk until he weaned himself off, but we did introduce it when I wasn't feeding him to help with that.
Other than that, hope that helps. Good luck!
A. B