Honestly, I wouldn't say this translation is correct English, "She and my". I've never heard 'she' followed by 'and' before. Now I don't know if this is an American 'thing'. They refer to each other as he and she without saying their name. But I think this is different.
I've SMS my partner to see what she thinks, she really wise up on English and she American.
I think you misunderstood the sentence. It's not about HER father. It's about MY father. If we group a father and HIS sister we can call them siblings (fratelli)
- Lei e mio padre sono fratelli = She and my father are siblings (OK)
- Suo e mio padre = His/her and my father (wrong, see my answer to markusfarry)
- Suoi e miei padri = His/her and my fathers (wrong in several ways)
- Her father = Suo padre (not found in the sentence)