Hi there,
If you believe in Chinese herbal medication, do try "Monkey Dates Powder" from Yu Eng Seng (Central, QRC), opposite to Wing Hang Bank.
Anyway, avoid cold & sweet drinks for your daughter. Warm water is best for her.
Best, of course, is send her for swimming classes in next Summer to allow her breathing system to get strong.
My 2 little girls are taking vitamins now, seems to be improving.......
Take care,
Fafa