Your AW has chosen this cheer-leader as a friend, probably specifically because she supports her decisions regarding drinking etc. I t doesn't really matter specifically how or why this woman supports her actions, odds are if/when she does start to question AW, AW will drop her as a friend and recruit a new cheerleader: that's what ExAH does.
I used to get really annoyed at ExAH's friends for not seeing the situation, for giving him emotional strokes, for propping his skewed view of reality up, for going out drinking with him.
Thing was as soon as they threatened his world view they were discarded, or they moved away themselves. This woman is a symptom, she isn't the problem.