Since kids were dying from taking over the counter meds many medication companies have changed their formulas and they no longer work. I would suggest you talk to a pharmacist about what meds he thinks would treat the symptoms your child is having.
I give the kids real liquid Sudafed for sinus congestion. If the goo is sticky and not coming out it is draining into their lungs like that and that makes them sicker. The fake Sudafed does not work. It only gives these kids the shakes and they are still congested. I can only buy it at real pharmacy's, the ones that are not chains, a family owned one perhaps. It is available at 3 pharmacies in my town and Walmart told me they didn't even make it anymore, I showed them my receipt and the bottle. Then they said they just couldn't get it anymore.
I use Walmart brand Tussin for chest congestion. It is a Guaifenesin syrup that is an expectorant. It makes the goo in the lungs runny so it can be coughed up. It is the SAME med that is in EVERY cough med except Delsym which is all DM. It does seem to work to stop coughing but does not work in the kids here for more than a couple of hours.
Dry hacking cough:
So, if your child is not having a productive cough she needs to have moisture in her lungs to loosen it to get it up and out. She needs to cough so it will not stay and live in her lungs and turn in to pneumonia.
Take her in a hot steamy shower several times per day, make sure their is moisture in the home, maybe a humidifier, if you can take her to the doc he may prescribe some nebulizer breathing treatments. They are usually mixed half med and half sterile water. This will help her by opening up her airways in her lungs and then the sterile water part of the med with moisten the goo. She will cough and cough after this and should have a more productive cough. It might take 2-3 of them if she is really really dry. Sometimes the doc will prescribe a steroid too. This reduces the inflammation in the airways and keeps them open longer. They have side effects of insomnia and behaviors so give them a long time before bedtime if possible.
Moist runny cough:
She needs to get a prescription for a med like codeine or Tessalon Perle's ( can you say very very very expensive?). They both relax the longs and then stop the cough reflex. The codeine is also an expectorant so it helps both ways.
I don't have this kind very often so I don't know a lot about it, just don't do anything to dry it up too much or you end up worse off.