As I was going to post my answer, I saw your second post. If she is thin, it may call for more love and attention than discipline. I would definitely change over to a concentrated, meat based chow if not feeding one now. This is an usual situation. You have a poorly socialized dog that went through losing its litter of puppies and then put in a new home. You might try a puppy chow. They provide a very rich diet, dense in calories. They are still going to be much closer to the diet she needs. Most breeders feed a puppy chow through pregnancy and lactation. Shouldn't hurt her for a while.
No website based on cups and pounds can as accurately determine the right amount food as the chart I posted above. Likely, it is a more general thing that as on your chow package. Most websites do not have access to as good of info as where I get mine. Many of them are dreadful.
1 Early socialization is very important. That is what is to be expected of a dog that lived in a kennel when young. The prominent behaviorists agree dogs may not be comfortable around things they are not exposed to between 6-12 WEEKS. Before 6 weeks they won't pay much attention to anything but mother and litter mates. After 12 weeks, their personality is set. Closer to the real world. I turned Sheba into the dog guide school in November. The waiting list is about 6 months now for another puppy. I got a call and we picked up Nita a week later. Somebody backed out of taking a puppy 2 weeks before Thanksgiving. The school sat down and started calling people. I was the first one to say we would pick up the puppy by the weekend she was 7 weeks old. Not only do they want the puppy in the home, but out in public, around traffic, strangers, noise, etc.
Give her more time to build a trust in you. Do not force her into uncomfortable situations. Strangers baring treats work well with food motivated dogs, but maybe less well with her. If she tolerates it, you invite people to pet her. She will never be like my puppies that know no other life than loving the attention they get from strangers.
You might check the King Charles Spaniel Breed description at American Kennel Club - akc.org
. Not all dogs are typical of there breed, but whatever most of them are like is what is typical of the breed. There are links to groups there too.
2 After 8 days, she should be starting to adjust. Have you had her to a vet? Take the medical records the breeder should have given you. You need to be setting up a relationship for routine care.
3 I would stick to the dry chow the breeder was feeding unless it is outlandishly expensive or hard to find. Normally a healthy dog can be disciplined to eat all the dry kibble it needs. Boiled rice and chicken is a standard bland recovery diet for a dog with an upset digestive system. It is not the complete and balanced diet they need long term. She has been through a lot. She may still need to lose some of the pregnancy weight gain. Unlike many Labs, she may be working at it herself. Ask the vet how her body condition compares to your interpretation of this chart:
September 07, link to chart replaced with LongLiveYourDog.com - Life Span Study - Rate Your Dog
It is off a dog food bag, but it is an illustrated version of what is in my dog guide school Puppy Raising Manual. Nobody, except the maybe the dog food companies, knows as much about the care of dogs as the service dog schools. I trust then more. If your dog dies, Purina will not spend the price of a nice car training you a new one before giving it to you. Unless she is under weight, tempting her with rich food is the wrong way to go. That leads to an overweigh, picky, dog with health problems. This is what you need to do. Put down the dish with what the dog should eat, and give it 15 minutes to eat. Then take it up. Do not give it anything to eat until its next scheduled meal. In a few days, it should be eating what it needs. Continue to check its ribs and adjust the food as needed. This is not easy. I had a Shepherd go 3 days on a few nibbles. I was a wreck, but she was fine. It is almost unknown for a healthy dog not to eat what it needs. Unfortunately, in too many cases, it is less than the package says, and less than the owner thinks the dog should have. Many dogs are quite good at holding out for tastier chow. Like kids, sometimes it calls for tough love.
4 Unless the dog's ribs are showing, this is far more serious than the food. Did you ask the vet about it?