Ask to see her current rabies certificate, (they need a vac. every 2 years), and that should be the end of it. FWIW, the chances of a domestic dog in the U.S. having rabies is close to nil in this day and age.
I'm assuming from this post that you don't know much about dogs, (nothing wrong w/ that), but the owner definitely should have known better. Any mother dog, (or cat/raccoon/monkey/etc..), is going to be naturally protective of the litter. Bringing a strange male, (I'm also assuming that she did not know you previously), into the lair was stupid. Showing puppies needs to be done w/ care, sometimes you need to separate the mother from the litter for a minute to do it. That bite was a pure protective move, she was scared of or threatened by you.
Bummer that it happened, though. I hope it does not sour you on dogs for good, they are wonderful creatures but still animals so they will occasionally act on instinct.
