Well, his office personnel would probably fall under a degree of confidentiality as far as revealing anything specific about his medical leave. But he is free to be as specific or not as he wants to be in response to inquiries from anyone. Whether or not she should directly ask him really depends upon how she views their relationship. He doesn't owe her any explanation, but I'm sure he's thought about how he will address inquiries from clients. I don't think she need fear expressing a general concern, perhaps coupled with an expression of hope that he's feeling better. Then he can respond as he wishes. I do think she can't demand more info than he volunteers, but that would be true for any relationship.