Potty training rescued dog

[adventurea]

We just adopted a year and half boarder collie mix from the SPCA. She is a joy, but we are having issues with her peeing in the appt. We take her for walks regularly throughout the day, and sometimes after those long walks she will still wait till we get back home to pee in the house. When I walk her I give her time to sniff as long as I can see it's not garbage and we stop at 'the pee spot' just before we come back in and let her sniff around for a good minute. We clean up when she does and take her for a quick walk to the pee spot and back.
She is fixed and had a full work over when she was at the SPCA so a medical issue shouldn't be the problem. She is a relatively calm dog and isn't nervous in the appt.
From what I have been reading we should clean where she goes in the house with vinegar and water. Is there anything else we should be doing?