How Do I Help My Little Sister With Her Persistent Cough?

Question

My sister who is eight years old has been experiencing a lot of breathing problems for three or four days. She has been coughing persistently and seems breathless. She does not seem to cough up any phlegm but her coughs are not really completely dry also. My mother first tried giving her Benadryl which gave her no respite. So she was put on Robitussin Cough formula by my mother but that was also totally ineffective for her. I tried telling my mother that she may suffer from asthma like me. She is finding it very difficult to breathe and is also suffering from a sore throat. I went and did a thorough spring cleaning in her room so that she may by chance get better with it but she is still the same. We have finally decided to take her to the doctor but I would like to know whether there is something to be done to give her at least a mild relief from the horrendous symptoms that she is experiencing. I would be very grateful if someone could suggest some solution as soon as possible and help my little sister out of her desperate situation.