V.W.
Cool mist humidifiers can help. Many resources suggest steamy air (like in a bathroom) but that never did anything for my son. Only cool mist, like nighttime outdoor air or from a humidifier.
I believe that the treatment protocols for cough may have changed for little ones. I know it seems like they were removing a lot of the OTC medications from the shelves, so maybe there isn't anything really worth giving her? I'm guessing on that.
As long as she doesn't get stridor (the pulling in of the ribs and skin around her chest/neck when she breathes) then she should be okay. Did the doctor show you what to look for? When my son would get it (every winter for several years until he was bigger--like age 5) it usually lingered for several nights, getting slightly better each night. But not usually more than about 3. But his cold would still be there.
Croup normally only affects them at night (not sure why, but that is the norm). Even if she is coughing, it may not be croup... just a cold with a bad cough at this point.
I hope you guys get some sleep.