Who would I contact regarding my mother's HUD apartment building and it's unacceptable living conditions?

County health department might be an option. If you want a higher profile response, local tv stations often like to help people who are exploited. But it's a question whether publicity will accomplish or antagonize.

Like aid, the local housing authority. HUD is suppose to examine these places before the person moves in.

Have you discussed this with the management company of the apartment at all? If they don't know about the problems they can't fix them.

Start with the housing authority in the municipality.

Messages to the local politicians, Secretary Ben Carson as well.