95 caravan stumbles and dies

I just got my close friend a 95 caravan from a friend at church she lives in NC I'm in sc, anyway she had discovered last week that it would stumble and die sometimes at idle sometimes while driving long distance (hr long or so) it has a mild skip and kinda rough idle, it throws the codes 12,21,23, during the long runs light stays on, I have read the o2 sensor can kill the engine if bad, that I'd a first for me hearing that, based on the info I have and codes I have does anybody have a similar situation and solutions? A direction I can go in without Throwing parts at it anyet information that can help me help her is greatly appreciated