Hi there
Have to agree with redcrx that it could well be hayfever. I got it out of the blue one summer when I was 15 and I am now 32 and still suffering!
When you say 'painful' nostrils though that could be something she may need to see her GP about. Hayfever can cause itchy nostrils, itchy throat, itchy eyes, sneezing, runny or stuffy nose but if she is in actual 'pain' then it might be something else.
Did she use a particular product when she had the cold (such as Olbas Oil or a decongestant?) - if she overused such products, she may well have damaged the lining of the nostril, in which case, she would need to see her GP.
If all the symptoms appear to be hayfever though, then watch out for seasonal changes (ie When it's humid and the pollen count is high does she suffer more with this problem?). In winter time do the symptoms subside completely?
I hope it's something that can be treated though and not hayfever. If it is, I'm afraid, summer's will never be the same again :o(
On a positive note, there are tonnes of products on the market to help.
All the best.