What kind of IBS does your friend have? IBS with diarrhea, IBS with constipation, or IBS that alternates between diarrhea and constipation?
I have IBS with diarrhea and I just don't drink alcohol anymore. Before, I'd have a drink or 2 on the weekends, but I'm not wanting to "rock the boat"...plus, my GI specialist has me on a couple of Rx for it.
My advice, if you have IBS, aviod alcohol...until you find out what's going on. It just isn't worth it.
You should have your friend join this message board. It really helps to discuss your problems, feelings about IBS, etc. Eveybody is really nice and understanding here.