I agree with CipherBot. I'll add another possibility (I'm pretty sure it wasn't mentioned in that previous question). You could say, "It's my cat and Louise's" or "It's Louise's cat and mine."
– chasly - supports MonicaSep 16 '15 at 13:08
Thanks Chasly. From the "duplicate" question - I take it that "It's Louise and I's cat" would be ok. That sounds wrong to me. I think the other answers indicate that "It's Louise's and my cat" is also fine.
– GeoffSep 17 '15 at 13:50
If the sentence "It's Louise and I's cat" is suggested then it is completely wrong! However II would certainly accept "It's Louise's and my cat".
– chasly - supports MonicaSep 17 '15 at 13:58