If the fever isn't high, she can try a lukewarm (not cold, but not as hot as her body) bath. If after 20-30 minutes, the fever doesn't come down, go for acamol as RachInbar suggested.
Natural remedies can be very dangerous, especially during pregnancy. Don't take any natural remedy without consulting a doctor!
Even something "gentle" like fennel can harm a pregnancy in high doses. (this doesn't mean a single cup of fennel tea or a salad with fennel is dangerous, but it shouldn't be used to "medicate" every day.)
Chicken soup, by the way, is a food, not a natural remedy.