My nan is insisting on keeping windows open during heatwave

Its literally 36 degrees outside and my nan keeps opening all the windows because "its too hot". I keep trying to explain to her that opening the windows only makes it hotter inside but she keeps insisting that keeping windows and curtains closed doesnt actually work. Its more frustrating because we live in a top floor flat and obviously heat rises so she really is just letting all that hot air from outside in.

On top of that i'm autistic and on antidepressants which makes it harder to regulate my body tempreature and i also have hypoglycemia which gets worse the hotter i am. Ironically the hypoglycemia is the whole reason she is staying with me in the first place as we are struggling to manage it at the moment and after a scary trip to a&e not long ago me and my mother decided it would be best to have someone with me in the day should worse come to worse.