HIPPA and client death

I received an email from an adult Client's mother informing me of my client's unexpected death. She sent me the obituary and replied to an email I had sent to client. I would like to respond and offer condolences and share how much I enjoyed getting to know her child. Is this ethical? If feels wrong not to reply at all. What would be the appropriate response? I'm also taking care of myself and processing my own emotions around this. Thank you