
I'd not be overly concerned about the common relative to be honest. Most breeders will 'linebreed' to fix type. It's knowing when an outcross is needed that's relevant, and making sure all the available testing for the breed, is done. It's inbreeding that should be avoided - ie mother to son, father to daughter and sibling to sibling. The KC advises (or used to?) a breeder talk to experienced fellow breeders if thinking about half brother to half sister.
As the owner of the stud dog is 50% responsible for the puppies he sires, if she's okay about letting you use her dog, I see no reason not to use him, provided he is also tested! But being local to you, wouldn't be a reason to use him, necessarily. We travelled for 12 hours by road, to get to the dog I wanted to use at one point.