Another wormie question - help!

My sister's dog is coming over tomorrow for Thanksgiving and I am scared she will get the worms that Casey has. The vet told me to make sure my sister's dog doesn't go near Casey's poo or in the general area that she usually goes outside. But I am scared that Casey will infect her if they are playing! Help!! They cant leave her at home (my family is coming to my house in NJ and they live in Queens) - its too long without having someone to walk her.