You can respond by saying: "I'm sorry to hear that your daughter has been sick. Is there anything I can do to help? or How is she feeling now? " or "I hope she gets better soon. Let me know if you need anything." This shows that you are concerned and willing to help, and it also allows the person to share more information about the situation if they choose to. Additionally, you can also express your empathy and concern for the person's well-being, and the well-being of their daughter. It also shows that you are listening and paying attention to what they are saying.