Re: child with cronic cough only at home
Put the new mattress outside in the sun and let it air out several days or couple weeks. Put the headboard outside to air, not in the sun.
It will take time for chemicals in those items to be released.
Air out her room real good and see if her coughing stops after those items have been removed.
Closing up the headboard in plastic is only holding the fumes, it needs to air out.
Same with the mattress.
If you have another bedroom for her to sleep in for a while will also help determine whether it is the new mattress and/or headboard.