I've had a degu with a cataract. He lived with it with no problems for most of the time, and he had adapted to it. His wasn't really white in colour either, it was more grey and sometimes very difficult to see.
Since your baby has it a a young age, she will probably grow up not knowing much difference, and will cope well with it. I'm sure she'll adapt!! There is plenty of advice out there for degus with cataracts because it is such a common degu problem, such as not moving the parts of the cage around or changing the layout as it will confuse her. It has also affected my degus sense of distance (when he jumps, it occasionally goes a little wrong), but they are hardy little creatures that cope quite well.
I will point out though, (and this may be a one off so don't worry) that my degu with cataract was prone to infection in that eye (i think he forgot it was there or something!?!), and has since had to have his eye removed due to really bad infection, despite numerous vet visits. He is now very happy with only one eye and copes marvelously!!!
Please try not to worry too much about her cataract, if that is what it is. She will adapt, and providing it doesn't go bad or nasty, i don't think you should worry. You sound like you've got the diet sorted, so keep with that and you'll not have to worry about sugar being an influencing factor. Genetics sounds like it is the culprit here!!
Good luck and keep us posted!!