I read your question carefully and I understand your concern.
The primary progressive form of MS your mother has unfortunately is the worst form of MS, for which no effective course changing treatment has been found. Treatment is limited only to alleviate symptoms and
physical therapy.
Manifestations of MS can be multiple according to the affected areas and if your mother has had the disease for a long time chances are she's at an advanced stage with many neurological deficits. One of the features of these neurological deficits is
spasticity which I guess is the cause of what you call spasms. Bilateral damage or involvement of
brainstem could also cause difficulty swallowing.
As for fever that could be as a result of an infection. Most common infections in MS patients are
urinary tract infections, but in her case with difficulty swallowing there is predisposition to aspirate secretions in her airways and have respiratory infection. So to find cause an urine analysis and chest x-ray is indicated.
Symptomatic treatment for spasticity usually is with a drug called
Baclofen while for the infection with antibiotics according to the type of infection that will come out in tests.
I hope to have been of help.