It's very hard to diagnose online .. we are patients on this community but want to welcome you to our community. I'd talk to her doctor about this .. she should be evaluated and a checkup is what I'm thinking. It may be from post nasal drip ? which can trigger asthma or asthma like symptoms .. have you tried an over the counter lozenger like a coughdrop to keep things moist. . . sometimes that takes away the tickled effect which triggers the cough.
Welcome to our community!
That is how my asthma/reactive airway problem started, constant coughing mainly in the mornings.
Postnasal drip, asthma, allergies (which can cause both of those problems), GERD, enlarged adenoids/tonsils can all plan a role.
Try over the counter cough medicine for 4-5 days and see if that helps (did nothing for my allergy/post nasal drip/asthma cough). Vicks vapour rub was the only thing that would let me sleep for a while back around christmas (before I was diagnosed).
If allergies are a problem you can look into using a sinus saline rinse (one type is a neti pot) that I found works wonders for my cat/dust mite allergies.
And of course, if nothing is helping over the next couple of weeks you need to go and get checked by a doctor as annoying as it is :)