I read the second her as meaning the partner is female.
I read the second her as meaning the partner is female.
You could be right. I took the "her" to mean his sister lived there with her partner and "her" daughter, as if the man she was living with was not the father of her daughter. I hope you're not confused, because I am. LOL Suffice to say, she's living with someone who she is not married to. ;o)
OK, another piece says:
"..Simon’s sister Helen has two children, aged eight and three..." So the daughter is Helen's and the sex of the partner is not identified.