This would be heat sickness, yes.
If you can, try to install an air conditioner in your home. If you can’t, improvise with a fan, a tub of water (which your glaceon will need to freeze), and perhaps a bag of ice. Give her plenty of cold water to keep her hydrated, and try to give her cooling foods (lettuce in addition to cold meats) to help keep her temperature down.
Whenever possible, you may wish to take her to the Pokémon League now and then. The facility is located at the top of Alola’s highest mountain, and as such, it’s perpetually covered in snow. The break will be good for your glaceon, and you might run into a potential ice-type partner that will work with her to keep her temperature down at home.
Best of luck!