An examination by a physician is the best way to have this evaluated and diagnosed.
You have only mentioned two symptoms:
1) A popping sound in her head. Since it is not localized to one or the other ear, and you don’t mention tinnitus (ringing/humming/buzzing in the ear), decreased hearing, or vertigo (spinning dizziness) it is not likely an inner ear problem.
2) She feels hot. Does she have a fever? Has she taken get temperature or if others touch her does she feel feverish? OR is it that she feels like the room is hot and she can’t get enough air? Since you don’t mention the above ear-related conditions, as well as no mention of pain or pressure in the ear(s), it is not likely to be a middle ear problem.
I am an Audiologist, and therefore only ears, hearing and balance are my expertise, which is why I’ve addressed those (and also since @grumpyfish suggested an inner ear infection).
When she does go to a physician, it will be beneficial for her to be able to answer the questions I’ve asked and to mention any and all other symptoms – even if they seem unrelated. I’d also be sure to mention any medications, dietary supplements, alcohol, caffiene, and illicit drug use.
Based on the extremely limited information you’ve offered thus far, my gut instinct is suggesting something more systemic, like endocrinal/hormonal, which can be influenced by what we eat and drink.