permanent blocked nose

My 14 year old sister has recently grown out of eczema (about 6 months ago). She has never had any other allergies, but since getting rid of the eczema she has had a permanent blocked nose, and what appears to be mild hayfever. It doesn't cause her any pain, but makes breathing through her nose very difficult. She doesn't have a cough, but does sneeze quite a lot.
We have tried the usual cold remedies, steam, hayfever tablets, and nasal sprays, none of which have worked.
Would be grateful for any ideas as to what this could be, and any treatment suggestions.