The best advice I would offer to you Justjenny is to listen to your friend and actually NOT offer any advice. Until you have lived with the turmoil and chaos of an alcoholic relationship you cannot imagine what it is like. Your friend will very occasionally see the kind and gentle man she fell in love with all those years ago and that is probably her reason for staying in the relationship. Has she tried Al-anon? I found that group very supportive and helpful. After 21 years of marriage and 2 children and now 10 years apart my ex and I are very close friends. I could not live with him again as he, like most addicts, is a manipulator and liar (getting less and less) but a loveable man nontheless. Be there to listen to your friend but any decisions need to be hers...let her cry on your shoulder and offer her a safe place to take refuge should circumstances ever need her to get out for a break one day.
Hope things turn out well for her in the end.