She may have. But for many years whiskey was commonly used and used safely (as in my case, my mom’s case, my husban’s case etc etc etc).
However with that level, it sounds like she wanted the baby to sleep (some women give their babies Benadryl for the same reason which can be abuse as well) rather than just help with the teething.
Thing about it was Mom had more than one set of teething rings. Several in fact in the fridge. We’d have one in our mouth then when that melted, put it back to re-freeze and get another. Never heard of using alcohol to do the job, just cryogenics.