You don’t necessarily know for sure that she doesn’t have a condition, she may have one but feel uncomfortable disclosing it, or as of yet is undiagnosed. Alternatively when she says it is nothing and that she’s okay, she perhaps means that it has a benign cause and therefore nothing for anyone to worry about.
Reasons for chronic cough could be anything from post nasal drip, asthma, acid reflux, tic, infection, medications, lung diseases, and early stages of dysphasia (swallowing problems) that may be a part of an underlying neurological disease.
90% of chronic coughs are caused by post nasal drip, asthma and acid reflux.
I feel the likelihood of it being a desperate attempt for attention wide off the mark and unfair, as her only crimes are liking to talk and snacking.
I also have empathy for those sensitive to noises or struggle with attention and focus through no fault of their own either. It’s a tough one, but i would have to side with the person who can’t help this and/or do anything to minimise it. The only thing that can be done, is try minimising the effect on you. Which could be lessened by ear plugs, air pods, ask to be moved furthest away from her.
I am pretty sure she can’t help it, and as someone already said it may well bother her far more than those around her and also cause her great embarrassment.