If my nieces wisdom teeth are coming in, can it cause fever, sore throat?

No: Not unless they are getting infected.

Gum tissues around: Erupting wisdom teeth often are sore and infected. If the infection becomes more serious, systemic infection could result with fever. Sore throat could also be related. However, there could also be a non dental concurrent issue unrelated to the third molar problem. Get her to her pcp and to her dentist for evaluation of both issues.

Yes: Chances are there is some infection going on in the gum tissue around these teeth. At her age if the teeth are just starting to come in, chances are she doesn't have enough room for them. She should see her dentist about having them removed. She may also need an antibiotic to help with the infection.

Signs of infection: Those are signs of a clinical infection of some kind. Unless the gums surrounding the wisdom teeth have developed an infection, it's probably not related to the teeth. It would be a good idea to have a dentist check it out to definitively rule out the wisdom teeth.