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Her neck is only sore at the sites of the swollen glands or are the neck muscles also very stiff/sore?
Any oversensitivity to looking at light? Any bad headache?
Could you please ask her to do a simple test? Have her try to touch her chin down to her chest. Please tell me if she is unable or unwilling to due to neck pain.
Very good--that means that meningitis is unlikely.
The fast-resolving fever spike was probably due to a viral infection that her immune system recognized and reacted against. The swollen neck glands are her lymph nodes doing their job filtering out the infection. Fever is usually defined as a temperature above 100.4 degrees Fahrenheit, so right now she only has temperature elevation, not fever. At this point, there is no need for an ER visit.
I advise rest, adequate fluids (enough intake that she voids at least once every eight hours), and perhaps Tylenol or ibuprofen (e.g., Motrin or Advil) if she shows discomfort with fever. Remember that the fever is actually a protective mechanism--that is, the body is trying to make itself an unsuitable environment for the infection. If her temperature lingers above 102 degrees Fahrenheit (a moderate fever), you might consider a 5-10 minute lukewarm bath or shower with rapid towel drying afterward to gently lower temperature. Do not use alcohol baths or anything that would cause a chill as this might make her fever spike higher. If her fever reaches 105 degrees Fahrenheit, call her physician or go to the ER--this temperature is not dangerous, but it merits medical evaluation, especially if it occurs in the face of fever medication(s).
With a healthy immune system, most common viral infections are cleared in 1-3 weeks. Antibiotics only work against bacteria, not viruses. If she complains of a bad sore throat (especially one that causes pain with swallowing) or develops a rash with redness and/or a sandpaper-like bumpy contour, consider physician evaluation for strep throat.