I have lifelong middle ear problems of a similar variety. The drainage doesn't have anything to do with
vaping per se, but it could be caused by the suction created when she draws from it, like sucking on a milkshake. This leads to a huge pressure change in the mouth and nasal cavity that could lead to pressure changes in the ear. She may have a perforated eardrum (if it's small it won't lead to hearing loss, and it often doesn't hurt at all) and needs to see a doctor as soon as possible.
In my personal experience, I had a perforated eardrum from sleeping with a bad cold (seriously), because I tend to build up fluid in my ear as it is and it didn't take much. My case was much worse and there was significant hearing loss, though it was temporary.
Until she sees a doctor (did I mention that she needs to see a doctor? Because she needs to see a doctor!), is she using an automatic battery? Try switching to a manual so the draw isn't so hard.