Karleen, I like your answer: very concise and to the point.

1. First, I would thank the client for their trust in me through telling me how they feel. Then I would encourage the client to communicate directly with my coworkers in the future if a similar problem happens again. I would say to my clients that I believe all my colleagues are happy and grateful to listen to their feedback in order to maintain high-quality service for them. By doing that, both PSWs and clients would benefit: We are a team.
2. Depending on the nature of the issue, there are at least three things I can do to help provide quality service to the client. First, I would figure out their needs by listening to them attentively and then adjusting the service accordingly on site. Second, if health and safety are concerned, I would report ASAP to my supervisor because the client should come first. Third, if there is no risk factor involved, I would consider further communication with my coworkers or the supervisor to take advantage of the incident as a learning opportunity; e.g. at the occasion of a group meeting, I might raise the topic without mentioning any names.