My thoughts are.... follow your "gut feeling", but be sure that you are thinking logically with a clear head and not just being a worry wart. If the female is one that will be a new addition to your breeding program and is a truly a good deal, then make it happen
. Before bring her home have her thoroughly checked out by your vet. Keep her isolated from the new mommy and pups - the pups will be protected somewhat from immunities from mother's milk, but I wouldn't take any chances.
OR better yet, maybe someone can keep the new addition for you until the pups are old enough for their first set of shots