Thank you for your question.
I'm assuming that she is under the care of an obstetrician and she does not have any illness right now.
Pregnancy is a thermogenic condition and it is very common for women to feel warm but their temperature is normal and they are not I'll with anything else. As the pregnancy progresses they notice this warmth less and about 24 weeks onwards they do not find it unusual.
However, if she hasn't consulted her doctor she should do so to rule out an actual infection as fever in pregnancy can be associated with miscarriage or early labour.