Suggest Treatment For Post Nasal Drip

Hello,
I have a question about my mom.
She is a non smoker, did have second hand smoke with her parents. Has been smoke free for about 25 years. She has allergies and possibly post nasal drip. She is 40 years old-female.
My worry is, she has a very bad chronic cough. she's had for almost a year. She got checked out and they said she's fine. Only found 4 ungrowing nodules on her lungs. They say she could of had them for a long time and they just aren t going to grow. They told her it was allergies, possibly post nasal drip. But lately she has been having a horrible cough. I do see that whenever it is cold outside her cough flames up to be worse. I looked into post nasal drip and they said stress can do alot to you as-well. Recently her mother and sister passed away 15 days apart. It's been rough. So, i'm extremely nervous about my mother for the outcome of lung cancer because of this cough... she has only one sign of lung cancer and that is the chronic cough. I'm just so scared. And i need advice, Should i be worried? Please help me doc.
If any further questions please respond and ask.