hello, i'm watching a friend's fish and I think she's really sick. the first time i changed the water in her tank (using room temperature distilled water) she immediately started floating on her side. i thought she had swim bladder so i am fasting her for three days. she seems to be on her side less but is now floating motionless at the top of the tank for the majority of the day. she also is breathing through her gills a lot and eating bubbles. i tried lowering her water level so she could breathe more easily and got her a plant to rest on but she won't touch it. i also have purchased some aquarium salt but am hesitant to use it because i'm not sure how large the tank is, maybe 1 gallon plastic bowl (and yes, I am well aware that this is an unhealthy environment for the fish but it's not something i can fix and my friend says the fish has had no health issues until now.) is it possible that she's too cold? I bought a thermometer as well and it said the temperature is fine but i'm worried that she's cold. i'm scared to buy a heater because the bowl is plastic. these symptoms have been going on for about four days. i'm sorry this is so long but i am losing sleep over the health of the betta fish and i just want her to get better, any advice is appreciated!