what is wrong with my blue heeler

Question
we have a family of blue heelers,the mother / father and four of the children all living in the same house.

from the very beginning we have had an issue with one dog,because she seemed to be abit whiny as a young pup we named her "whimpy".

this name has suited her ,unfortunately whimpy has caused an array of issues with the entire pack,she will yelp if startled,she will not allow you to hold her for any length of time,she will begin yelping and pissing herself and deficate everywhere when these situations accur.

when she yelps the other females attack her ,seeing her as a weak link,its bad enough where we have to have one dog constantly on a muzzle around whimpy.

we cannot get her into a vehicle,the vet has to come to our house to treat whimpy if she is injured during one of these attacks.

the other dogs all seem normal,this is a pack order,normal behavior and they all listen except for whimpy,we love her dearly,if there is any medication that might be helpful for her condition please let us know.

Answer
First, you need to CHANGE THE DOG'S NAME.  She is not "wimpy", she is (apparently) disabled to some degree.  You carry a psychological identifier with your name: suppose your mother had named you "mistake"?  You may not be conscious of doing so, but attaching that identifier to a dog further disables the dog, in your mind.

Your dog may be suffering from visual, neurological or orthopedic problems.  And you do NOT have control of your "pack", or it wouldn't be necessary for you to muzzle one of your dogs (which, by the way, has most likely worsened the problem to the point where it may not be able to be rehabilitated.)  Keeping a full litter with the dam and sire is never a good idea; breeding (or allowing to breed) a pet dog is never a good idea; there's a great deal that goes into producing sound puppies from a litter.  This requires constant monitoring of development (weighing each puppy every day and supplementing if one is not gaining weight), overseeing the dam to be certain she is able to manage her puppies properly, carefully socializing EACH puppy AWAY from the others every single day beginning when they are three weeks of age; having the parents carefully screened for any inheritable traits BEFORE allowing the pregnancy, etc.  Once the puppies are on the ground and properly managed, establishing psychological management of this "pack" (who should never be raised together, you see the result) is mandatory.

Why has your veterinarian not recommended more appropriate veterinary care....MONEY and lack of integrity.  This dog needs to be carefully and fully evaluated by a veterinarian (and if this means she has to be sedated to be taken to the vet, so be it).  She needs a full blood chemistry, an opthalmologic checkup (this breed carries PRA, for all you know she may be blind or nearing blindness), an orthopedic check (for hip dysplasure, birth canal injury, or other problem acquired from interacting with the other dogs) and a neurological evaluation.  THIS IS MANDATORY.  If the dog's health checks out, then you must find a certified applied animal behaviorist who can come into your home, evaluate ALL your dogs, interview you and all other human family members thoroughly, observe interaction among and between your dogs, and do a temperament evaluation of this poor dog.  You need to be taught how to manage a "pack" and, if necessary (in the opinion of the professional), you may need to rehome one or more of them.  Asking questions on the internet will NOT DO IT.  You allowed this animal to come into the world; you OWE HER.  Do what's necessary.