As far as I know, although I could be wrong, a liver can't be trained to metabolise more alcohol per hour. Excess alcohol will always damage the liver, and only taking a good break from alcohol consumption will allow the liver to heal, assuming the damage wasn't too extensive. However, professional drunkards do get accustomed to alcohol, which means that even if they have a concentration of alcohol in their blood, they can still function far more normally than sunday drinkers. Of course there are individual differences in the alcohol tolerance, so some people choosing the career of a drunkard are luckier than others.
It seems to me like Noa only drinks during social situations, like going out to drink with Rihito, plus her work regularly keeps her busy, so with any luck she's not drinking enough to damage her organs.