hi ek, the visiting neighbor's dog is allowed inside the motor home (no, i'm no fan of a motor home, but camping circumstances dictate it) that i'm staying in. my significant other doesn't allow my dogs inside.
If the visitors dog is just a one off or a rare occasion, it could just be a courtesy being extended. And if your dogs being in there is an ongoing thing, then I wouldn't take it personally.
As a kid my dad didn't allow our dog in the house. There was the occasional visitor who'd pop over and bring in their (small) dog.
But it will depend on your specific situation. Have a think about it and if you still don't feel comfortable about it, voice your concerns with the significant other. The compromise might be that she has to tell ALL visitors to leave their pups outside.