Dit hovedsprog er dansk, så jeg går ud fra at du ved at din anmodning ikke er på dansk. Kan du fortælle mig på hvilked sprog din anmodning er skrevet?
She could say "my precious/gold" but she wanted to put the accent on that she is his sister and he is her brother. She is using 3rd person singular for herself - "sister".
I guess there's no other way to translate it and not to sound strange...
She is not telling him that he is her gold but calling him like that. But than again from the way she's calling him we can conclude that she wanted to tell him that.