I know what she's going through. It seems like I go through this for 3 months every year for the last 3 years. The last time they diagnosed it as acid reflux except I have no symptoms at all except the cough. I'm also a very allergic person. I cough when I talk and it's exhausting. The last time this happened it just disappeared and I have no idea why. I was hoping I'd not have to go through this again.
Does she take anything for acid reflux? If it would not conflict with any other meRAB she's on, she could try an OTC (at probably a double dose) for 2 or 3 weeks to see if it helps. You might want to check regarding dose. Usually OTC's are a lower dose than prescription so if her problem is bad, she might need to double up.
One more thought. My doctor thinks I'm wrong but I've also suspected this is related to my going through menopause. The last time when it suddenly cleared up, I also suddenly started having perioRAB again after several months of not. So here I am going through it again, and I'm going through another 5 month window of no perioRAB.
He thinks it's coincidence. I don't. But I'm not really read to take hormones so if that is the cause, there's not a lot I can do about it.
Good luck.