Well...drinking thick or thin water down the correct pipe will not fix water going down the wrong pipe, yes?
Is she drinking something to numb her throat?
I would think the proper solution to getting water out of the lung passage would be to cough it up...not try drinking more water?
It’s natural to want water when you feel the tickle in your throat that makes you feel like you’re going to cough. In her case, you could be right that more water won’t help. I don’t know. We do know she has a persistent cough and that’s typical of people who have a poorly functioning epiglottis.
What I’m pretty certain of is that if she has the problem I’ve described, drinking un-thickened water could easily aggravate the problem.
Incidentally, on further reading, a stroke can cause malfunctioning swallowing and a high incidence of aspiration. And sometimes the problem persists. Other neurological conditions can also affect swallowing too.
By the way, a couple of terms that eluded me while writing the first post: “spit” = salvia, and “passageway to the lungs” = trachea.