Possible altitude sickness?

every time my girlfriend goes up to see her family in illinois (we live in mississippi currently), she gets pretty sick, she gets light-headed, nauseous, she vomits a lot, bad migraines, sometimes fever, and very weak. we think it could be high altitude sickness, we're not really sure, any suggestions or help would be great, and a suggestion as to what medication to help would also be great, she doesn't have car sickness if you were wondering, she takes dramamine on all her car trips, and this trip to illinois is the only trip that it doesn't help. Best answer will be chosen thank you.