Taking medication with alcohol is never a good thing, especially if the drinking results in a binge. If your wife drinks occasionally but when she does drink - she can not stop, she may be a binge alcoholic. This condition is as serious as if she were a daily drinker.
Alcohol intoxication does initially seem to help anxiety and depression which is why people often drink. They may use it as a form of 'self medication'. However, this effect does not last and anxiety and depression are often made worse. If your wife was prescribed Paxil, I am guessing she has been diagnosed with anxiety or depression. Drinking would counteract any help the Paxil will give, as well as possibl worsen her condition.
Taking Oxycontin along with alcohol is very dangerous. If your wife is bingeing on alcohol, she runs the risk of an overdose. Both drugs are depressants and when working together, can have a synergistic effect - a compound effect that leaves your wife at risk. My suggestion to anayone taking opiates is to not drink or if they will drink, to not take the opiate.
You are right to be worried. I would suggest that your wife speak to her doctor and to tell the doctor just how much she is drinking so that her doctor can prescribe a safe protocol of medication.