Sounds like apt A is correct. The co-op needs to do something. It's possible that Z's renovation was a sub-standard job since A can now smell other things that they did not smell prior to the renovation. The plaster dust piling up on A's floor is a health hazard at a minimum and needs to be addressed immediately.

I recommend that the co-op hire someone to check the integrity of that shared wall. If it needs to be repaired, then do it ASAP. and let the co-op pay for it.

It's possible that the co-op can try to collect the repair money from Z's contractor, but the co-op will need to show that it was a shoddy renovation that caused the extra smells and the piling of dust. Good luck.