Sorry, to hear this. It sounds so bad, but maybe do not think the worse till you get a diagnoses. She is very young. please let us know how she does. sory i cant be more help
Please do try not to worry if you can. I know that will be hard, as you love her, and she is in pain, but try. It will also help her to feel calmer.
What makes you feel this problem could be cancer? It might very well not be. Yes, she does need to see the vet as soon as you can get her to one, as she is obviously in pain, and something is very wrong in her neck and chest. But it does not necessarily sound like cancer. There are so many other things this could be. It is very common for dogs to be off their food if they are feeling pain. Also it is common for them to not want to move, as this will make the pain worse. I am sorry, but I cannot tell you exactly what her problem is. Try Ghilly, (on this forum) She knows an awful lot about many things. or "Ask a vet" page, if you can get through to post.
Do try to get her out to see a vet or get a vet to visit you, as soon as you can, if that is at all possible with the weather conditions you have. I hope that my answer is some help to you when you are so worried, and feel so helpless because of being snowed-in right now. But the only thing I can say is, this does not necessarily HAVE TO BE cancer.
Is there a possibility your dog could have been bitten by something? Do you live in an area where there are poisonous snakes or spiders? I know you said you were snowed in, which would eliminate the possibility of her having been bitten by something outside, but if something had gotten into your house and managed to hide in there unnoticed, is it possible that she could have found it? Can you see any obvious bite marks on her anywhere?
Then, too, it could be some type of cellulitis. There is something that is usually referred to as "puppy strangles", which is also called "juvenile cellulitis", caused by streptococcus bacteria. Juvenile cellulitis usually strikes puppies between the ages of about 4 weeks to 16 weeks, but the possibility of her having picked up streptococcus somewhere (a small break in the skin perhaps?) and having it develop into this type of swelling came to me as a possibility. Juvenile cellulitis is treated with antibiotics and corticosteroids.
I don't think this is cancer, I can't think of any type of cancer that would manifest itself in this way. It really sounds to me like she is having a reaction of some sort to something or she has developed an infection secondary to some type of injury or bite. Think as hard as you can and see if you can come up with something that she could have gotten into, or something that could have gotten her.
Ghilly