The medication she is taking is a common, and powerful combination. there is not much room for improvement. The alcohol is a problem and needs to be treated separately in some form of rehab. or psychiatric treatment. The potential bad effects are numerous, and serious, depending on how much and how often she drinks, but certainly there is a possibility of accidents at home, as well as seizures and blackouts.
Very complicated situation indeed. Mixing Xanax and alcohol isn't a good idea -- at least not in large doses since they have an additive effect. I've had a couple drinks here and there while taking xanax, and I'm still alive, but that's probably because the dose of xanax was mild and so was the alcohol intake. But if she is on a moderate to high dose, and she's drinking a pint of vodka/whiskey or 10 beers a night (whatever it takes for her to pass out) then that's a recipe for disaster. Mixing Zoloft and alcohol does carry nearly the same risk as mixing Xanax and alcohol.
In addition, the long-term effects of alcohol are very numerous and complicated as well. Oftentimes, alcoholism and depression are comorbid (they exist together) so it becomes a tough problem to deal with. Long-term alcohol abuse can result in alcoholic hepatitis (or even cirrohis), peripheral neuropathy, cereballar degeneration, brain atropy, and even Wernicke's-Kirosakoff's syndrome, if her diet lacks sufficient thiamine (B1). In addition, chronic alcoholism is bad for the heart and increases a person's likelihood of having a stroke. The depression here has to be aggressively treated.
What I would recommend is Effexor XR supplemented with Wellbutrin. This way, you have the best chance of warding off depression since these medications increase levels of serotonin, norepinephrine, and dopamine. As well, maybe a long-acting benzodiazepine like Klonopin would be beneficial to ward off the craving for alcohol. Perhaps even Antabuse if she's willing to take it, which will make her ill if she drinks alcohol. Make sure she eats well or at the very least takes a vitamin. Try to get her to ease up on the drinking. You need an aggressive psychiatrist to manage these symptoms. ASAP. Get this person help soon, because the way it's going, there isn't a pot of gold at the other end of this rainbow.