fear biting?

Question
We got a three year old female soft coated wheaten terrier last October. We
already have two wonderful male SCWTs from the same breeder when she
called and asked us to take Meghan. The breeder said that her health had
been failing for quite some time and she had been diagnosed with Lou
Gehrig's disease and therefore couldn't take care of her dogs anymore. She
was finding homes for all five them. She warned us that Meghan sometimes
bites the feet of people trying to come into the house.
We found Meghan to be very submissive and shy, but she seemed to gain
more confidence as time passed and is very affectionate to people she knows.
Then a friend of ours came to visit with her teenage daughter. We introduced
them to Meghan and everything seemed just fine. Then, out of the blue,
totally unprovoked, she came up behind the girl, bit her heel and then bit her
mother. We swooped down to remove Meghan and watched her carefully for
the rest of the visit. She attempted to bite the girl a few more times. My sister
and a friend came to stay at our house to take care of the dogs while we were
on vacation. Meghan met them, played with them, kissed them and then
turned into a monster and bit one of them on the ankle. Her mood changes
so drastically for no reason.
Today she bit me when I attempted to isolate her and the other dogs because
I had a repairman in the house.
Meghan gets plenty of exercise and interaction with other dogs and people.
She has a very solid routine and we give her lots of affection. We would hate
to put her in a crate every time someone is at our house. She really hates it
and spins around in it constantly. We asked our Vet about it and he didn't
seem to have any answers either. I am a bit afraid of her now because I never
thought she would bite me. I think she feeds off of the other dogs'
excitement over new people so it's hard to isolate her and correct her. I have
no idea how to solve this problem. Thanks in advance for any suggestions.

Answer
Not being able to see the dog's behavior, I have to give you my best educated guess.  It appears that Meghan is a fear biter; this is definitely NOT a dominance issue.  The SCWT can be a very high problem dog in terms of aggression, so this is not unusual.  What IS unusual is that any reputable breeder would have such a dog in a breeding program.  I guaranty you that this dog was either a kennel dog or very poorly socialized (if at all), which tells me that your breeder is not breeding for type and temperament and it's a very good thing that she's no longer breeding.  Ask any reputable groomer and you will find out that the SCWT is one of the least favorite among them.

Rehabilitating a dog with this problem requires hands on, in person evaluation by a certified applied animal behavior expert (NOT a dog trainer!)  You need to call local veterinarians, as well as the veterinary college in your geographical area, and ask for referral to a Ph.D. or DVM behavior expert with a lot (a LOT) of experience rehabilitating active dog to human aggression.  Even the bite you received is most likely redirected aggression related to fear, and this is how you handle any future possibility of it repeating.  Put Meghan on a house tab (long, lightweight nylon leash) when you are at home.  If you need to control her behavior in any way, pick up the leash by its handle, do NOT use your hands to her collar or body.  It's unlikely that Meghan bit you deliberately, it was more likely a reflex action to excitement/fear/anxiety, a redirected behavior.  At all cost, you must prevent any future reoccurrence, as dogs learn more about aggression with every bite.

In terms of controlling her behavior around visitors, this particular dog cannot be allowed to freely mingle with any visitors until you are in the care and supervision of an expert.  At best, she will bite again and learn more about using aggression to allay her fear; at worst, you will be sued.  Isolate her in a locked, well supervised (so no one can gain admission) room before visitors are expected.  Give her special treats and special toys, only for this purpose, and ignore any and all whining, scratching, etc.  Do NOT allow her to see or interact with any visitors, as this will exacerbate her fear and her aggression will escalate.

Give this dog behaviors you can reward her for by introducing positive reinforcement training, but use a visual signal (not a clicker) as the sound might alarm her.  Learn about positive reinforcement training by reading Ian Dunbar DVM, John Fisher, Patricia McConnell Ph.D., Paul Owens and going to Karen Pryor's web site.  Introduce one behavior using a made up word (not normal commands such as "sit").  Do this in short, multiple intervals throughout each day until you have a solid 100% successful response (ten out of ten), which could take up to two to three weeks (given that you are a novice.)  This will give the dog a way to please you, increase her trust in you, elevate your rank and begin to expand her cognitive abilities somewhat.  Don't try to handle this fear issue by yourself.  Find an expert.