Hi. My 4m/o daughter had a badrespiratory infection from secon hndsmoke (idontsmoke) now shes 6mos and is coughing kind of bad. Is it back? Or a cold?

Hard to say. Kids at that age are expected to have about 5 URI's per year and this could be a new one. Coughing is also a natural response to environmental irritants, so smoke exposure/fumes/perfume/cleaning fumes, etc can also be a problem.If her feedings and activity are off and you are concerned have her evaluated.
I would recommend. that you bring her in to her pediatrician to be checked. It certainly could be a cold, but if she is coughing, her chest should be checked to make sure she isn't wheezing and to make sure she doesn't have pneumonia. If she is not drinking fluids/eating well, or having difficulty breathing, it is important that you take her in today.