Dear Mrs. Tadaka,
I apologize for not writing back sooner. Your letter took me by surprise and I suppose it's taken me this long to process your words.
I can appreciate that reaching out after so many years was difficult for you and required much deliberation. As you can imagine, it is not a simple thing to give Haha unexpected news in her current condition. The last few years have not been kind to her health. There are days when she can be unstable... aggressive. We are not always able to anticipate what triggers her and for that reason, I would like to hold off on your visit with her for the time being.
I know that is unfair to ask you to continue waiting, but please understand that I am only trying to proceed with caution for her sake, and yours. In the meantime, I will keep in touch and would be happy to host you at Haha's house in Hillsborough, if you are open to it. I have attached my business card with my contact information. Please feel free to give me a call anytime.