I am concerned that your dog may be experiencing neck pain due to Intervertebral Disc Disease (IVDD, herniated disc). This happens when the material in the discs between the boney vertebrae in the back ruptures out and presses on the spinal cord. There is a lot of internal swelling when this occurs, leading to pain and decreased nerve function. This can happen in conjunction with arthritis of the vertebrae, because that causes decreased flexibility between the vertebrae.
In order to confirm this suspicion, your dog should go see her veterinarian promptly. If she has ruptured a disc, the sooner treatment is begun, the better the prognosis.
Treatment for IVDD often involves anti-inflammatories, pain killers and/or steroids. The goal is to decrease the swelling which in turn decreases the pain and improves nerve function. Sometimes, however, they are not enough. In these situations, surgery can be done to go in and remove the disc material that is pressing on the spine. This is called "decompression" surgery.
In order to determine what is appropriate treatment for your dog, a veterinarian needs to perform a very thorough neurological examination. The vet looks for neurological deficits such as a delay in turning the back foot over if it is turned so the top of the foot is on the ground instead of the pads, while the dog is in a standing position. The vet also looks for "purposeful movement" which is a stepping motion of the hind legs when the vet supports the dog's weight so the legs can swing freely. There are a number of other neurological tests the vet does to test reflexes. Also, the vet manipulates each vertebrae in a way to find where there may be pain.
Often, if a painful area is located, the vet will recommend x-rays to look for a compression between the vertebrae. This confirms the diagnosis.
The prognosis for each patient depends on the symptoms, the results of the neurological examination, how long the problem has been present, and how the dog responds to treatment.
I am concerned about your dog because it sounds like she is in pain. I would strongly recommend a visit to your veterinarian as soon as possible for examination and treatment. It would be helpful to take her on an empty stomach just in case they need to give a sedative/pain killer to take x-rays.
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Until you can get her to the vet, please keep her as quiet as possible, with just short visits outside to do potty business. Carry her up and down the stairs, as this is when the neck and back flex and extend the most, and further damage is most likely.
In terms of whether to go see an emergency vet tonight or not, you may wish to consider trying a warm compress at home first. Many people with back or neck pain report that a warm compress is soothing, and your dog may appreciate that too. You can do this by making a wet towel compress. Place a small wet towel, folded into a zip-lok bag (unzipped!) and heat for about 2 minutes in the microwave. Remove and press all the air out. Make sure it is not too hot! You may want to put another towel around it, and then gently place over your dog's neck.
If your girl is not finding any relief with these measures, and is unable to settle down for the night, you may need to see an emergency vet tonight. If, however, she does seem more comfortable, please do get her in to see her family veterinarian promptly tomorrow morning!
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Good luck, and best wishes for your baby! Please let me know how she does.