She should figure out how to drink and eat on her own with the cone on. It may take a few tries, and if you kind of show her how to get to the dish with it on it'll probably be faster, but she'll figure it out.
Also, I understand your concern about her quality of life with only one eye. But I agree with your vet, being as young as she is, she should do great, even with one eye
Dogs don't really see it as a loss, like we would perceive it with losing an eye. It may take a bit for her to figure out how to get around with just the one, and she may be spooked from time to time if you sneak up on her from that side, but other than that she'll just think that that's how she's made, and won't be any less happy because of it.
Maybe talk to her as you approach her, so she knows you're there. I can understand your anxiety, she's your baby
But I think she's going to have a happy life regardless if she has 1 or 2 eyes.
Hope this helped