Actually this is one of the few Hindi sentences which seems wrong without an article.
We would say - जूलिया की एक बच्ची/बेटी है।
There is however one situation where your sentence could work. If a child is playing and someone asks you whose child that is - you could say
(वह) जूलिया की बच्ची है। It's/that's Julia's child.
But female is never mentioned. I am not 100% sure why बच्ची has the ई ending, but I assume it has something to do with the fact that Julia is a female name and so it is assumed that the child (gender neutral form of child) is female. Since there is not a female/male conjugation for "child" in English, simply "child" is written.
Prime example of clear and open pronunciation of 'है' here; just came from another board for 'उनका घर भारत में है' where it was clearly pronounced 'हैं' and the difference is plain as day! I'm fairly convinced the other one needs changing - didn't have a report function for the audio either so I'm posting here too