myself having experienced this just before xmas last yr , coughing is part of a heart murmur , make sure you keep her cool as the heat will make her heart work harder , i also found that excitement would make my girl pass out .
the day i gave my girl her wings she was coughing constantly and had fluid in her chest and legs .
Things to watch for -
wobbly unbalanced walking
panting a lot
These are all the things i noticed with my girl , she was a grade 4 when diagnosed 2 weeks beforehand she was running ,swimming and playing ball at the beach , we had one really hot day when i was at work , when i came home she was all wobbly drunk like , it came on very sudden she had always had a clean bill of health , she was diagnosed that day , i got to spend 6 more weeks with her , the main thing i noticed near the end was the fluid build up , i do feel i left her a little to long , if i could turn back time i would have given her wings when her tummy started to swell ,a week after her legs started to swell and thats when she became much worse , 2 days after her legs i woke up and she was coughing constantly and couldn't walk without nearly passing out i knew i had to let her go
good luck with your little girl , i dont mean to scare you at all but its best that you know what you may be in for , i hope you get to spend a lot more yrs with her yet
edited to add
with her coughing more so now i would take her to the vet as i would say her medication might need to be a higher dose .